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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * User-space Probes (UProbes)
  *
  * Copyright (C) IBM Corporation, 2008-2012
  * Authors:
  *  Srikar Dronamraju
  *  Jim Keniston
  * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
  */
 
 #include <linux/kernel.h>
 #include <linux/highmem.h>
 #include <linux/pagemap.h>  /* read_mapping_page */
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/coredump.h>
 #include <linux/export.h>
 #include <linux/rmap.h>     /* anon_vma_prepare */
 #include <linux/mmu_notifier.h> /* set_pte_at_notify */
 #include <linux/swap.h>     /* try_to_free_swap */
 #include <linux/ptrace.h>   /* user_enable_single_step */
 #include <linux/kdebug.h>   /* notifier mechanism */
 #include "../../mm/internal.h"  /* munlock_vma_page */
 #include <linux/percpu-rwsem.h>
 #include <linux/task_work.h>
 #include <linux/shmem_fs.h>
 #include <linux/khugepaged.h>
 
 #include <linux/uprobes.h>
 
 #define UINSNS_PER_PAGE         (PAGE_SIZE/UPROBE_XOL_SLOT_BYTES)
 #define MAX_UPROBE_XOL_SLOTS        UINSNS_PER_PAGE
 
 static struct rb_root uprobes_tree = RB_ROOT;
 /*
  * allows us to skip the uprobe_mmap if there are no uprobe events active
  * at this time.  Probably a fine grained per inode count is better?
  */
 #define no_uprobe_events()  RB_EMPTY_ROOT(&uprobes_tree)
 
 static DEFINE_SPINLOCK(uprobes_treelock);   /* serialize rbtree access */
 
 #define UPROBES_HASH_SZ 13
 /* serialize uprobe->pending_list */
 static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
 #define uprobes_mmap_hash(v)    (&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
 
 DEFINE_STATIC_PERCPU_RWSEM(dup_mmap_sem);
 
 /* Have a copy of original instruction */
 #define UPROBE_COPY_INSN    0
 
 struct uprobe {
     struct rb_node      rb_node;    /* node in the rb tree */
     refcount_t      ref;
     struct rw_semaphore register_rwsem;
     struct rw_semaphore consumer_rwsem;
     struct list_head    pending_list;
     struct uprobe_consumer  *consumers;
     struct inode        *inode;     /* Also hold a ref to inode */
     loff_t          offset;
     loff_t          ref_ctr_offset;
     unsigned long       flags;
 
     /*
      * The generic code assumes that it has two members of unknown type
      * owned by the arch-specific code:
      *
      *  insn -  copy_insn() saves the original instruction here for
      *      arch_uprobe_analyze_insn().
      *
      *  ixol -  potentially modified instruction to execute out of
      *      line, copied to xol_area by xol_get_insn_slot().
      */
     struct arch_uprobe  arch;
 };
 
 struct delayed_uprobe {
     struct list_head list;
     struct uprobe *uprobe;
     struct mm_struct *mm;
 };
 
 static DEFINE_MUTEX(delayed_uprobe_lock);
 static LIST_HEAD(delayed_uprobe_list);
 
 /*
  * Execute out of line area: anonymous executable mapping installed
  * by the probed task to execute the copy of the original instruction
  * mangled by set_swbp().
  *
  * On a breakpoint hit, thread contests for a slot.  It frees the
  * slot after singlestep. Currently a fixed number of slots are
  * allocated.
  */
 struct xol_area {
     wait_queue_head_t       wq;     /* if all slots are busy */
     atomic_t            slot_count; /* number of in-use slots */
     unsigned long           *bitmap;    /* 0 = free slot */
 
     struct vm_special_mapping   xol_mapping;
     struct page             *pages[2];
     /*
      * We keep the vma's vm_start rather than a pointer to the vma
      * itself.  The probed process or a naughty kernel module could make
      * the vma go away, and we must handle that reasonably gracefully.
      */
     unsigned long           vaddr;      /* Page(s) of instruction slots */
 };
 
 /*
  * valid_vma: Verify if the specified vma is an executable vma
  * Relax restrictions while unregistering: vm_flags might have
  * changed after breakpoint was inserted.
  *  - is_register: indicates if we are in register context.
  *  - Return 1 if the specified virtual address is in an
  *    executable vma.
  */
 static bool valid_vma(struct vm_area_struct *vma, bool is_register)
 {
     vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_MAYSHARE;
 
     if (is_register)
         flags |= VM_WRITE;
 
     return vma->vm_file && (vma->vm_flags & flags) == VM_MAYEXEC;
 }
 
 static unsigned long offset_to_vaddr(struct vm_area_struct *vma, loff_t offset)
 {
     return vma->vm_start + offset - ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 }
 
 static loff_t vaddr_to_offset(struct vm_area_struct *vma, unsigned long vaddr)
 {
     return ((loff_t)vma->vm_pgoff << PAGE_SHIFT) + (vaddr - vma->vm_start);
 }
 
 /**
  * __replace_page - replace page in vma by new page.
  * based on replace_page in mm/ksm.c
  *
  * @vma:      vma that holds the pte pointing to page
  * @addr:     address the old @page is mapped at
  * @old_page: the page we are replacing by new_page
  * @new_page: the modified page we replace page by
  *
  * If @new_page is NULL, only unmap @old_page.
  *
  * Returns 0 on success, negative error code otherwise.
  */
 static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
                 struct page *old_page, struct page *new_page)
 {
     struct mm_struct *mm = vma->vm_mm;
     DEFINE_FOLIO_VMA_WALK(pvmw, page_folio(old_page), vma, addr, 0);
     int err;
     struct mmu_notifier_range range;
 
     mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
                 addr + PAGE_SIZE);
 
     if (new_page) {
         err = mem_cgroup_charge(page_folio(new_page), vma->vm_mm,
                     GFP_KERNEL);
         if (err)
             return err;
     }
 
     /* For try_to_free_swap() below */
     lock_page(old_page);
 
     mmu_notifier_invalidate_range_start(&range);
     err = -EAGAIN;
     if (!page_vma_mapped_walk(&pvmw))
         goto unlock;
     VM_BUG_ON_PAGE(addr != pvmw.address, old_page);
 
     if (new_page) {
         get_page(new_page);
         page_add_new_anon_rmap(new_page, vma, addr);
         lru_cache_add_inactive_or_unevictable(new_page, vma);
     } else
         /* no new page, just dec_mm_counter for old_page */
         dec_mm_counter(mm, MM_ANONPAGES);
 
     if (!PageAnon(old_page)) {
         dec_mm_counter(mm, mm_counter_file(old_page));
         inc_mm_counter(mm, MM_ANONPAGES);
     }
 
     flush_cache_page(vma, addr, pte_pfn(*pvmw.pte));
     ptep_clear_flush_notify(vma, addr, pvmw.pte);
     if (new_page)
         set_pte_at_notify(mm, addr, pvmw.pte,
                   mk_pte(new_page, vma->vm_page_prot));
 
     page_remove_rmap(old_page, vma, false);
     if (!page_mapped(old_page))
         try_to_free_swap(old_page);
     page_vma_mapped_walk_done(&pvmw);
     put_page(old_page);
 
     err = 0;
  unlock:
     mmu_notifier_invalidate_range_end(&range);
     unlock_page(old_page);
     return err;
 }
 
 /**
  * is_swbp_insn - check if instruction is breakpoint instruction.
  * @insn: instruction to be checked.
  * Default implementation of is_swbp_insn
  * Returns true if @insn is a breakpoint instruction.
  */
 bool __weak is_swbp_insn(uprobe_opcode_t *insn)
 {
     return *insn == UPROBE_SWBP_INSN;
 }
 
 /**
  * is_trap_insn - check if instruction is breakpoint instruction.
  * @insn: instruction to be checked.
  * Default implementation of is_trap_insn
  * Returns true if @insn is a breakpoint instruction.
  *
  * This function is needed for the case where an architecture has multiple
  * trap instructions (like powerpc).
  */
 bool __weak is_trap_insn(uprobe_opcode_t *insn)
 {
     return is_swbp_insn(insn);
 }
 
 static void copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len)
 {
     void *kaddr = kmap_atomic(page);
     memcpy(dst, kaddr + (vaddr & ~PAGE_MASK), len);
     kunmap_atomic(kaddr);
 }
 
 static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len)
 {
     void *kaddr = kmap_atomic(page);
     memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len);
     kunmap_atomic(kaddr);
 }
 
 static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
 {
     uprobe_opcode_t old_opcode;
     bool is_swbp;
 
     /*
      * Note: We only check if the old_opcode is UPROBE_SWBP_INSN here.
      * We do not check if it is any other 'trap variant' which could
      * be conditional trap instruction such as the one powerpc supports.
      *
      * The logic is that we do not care if the underlying instruction
      * is a trap variant; uprobes always wins over any other (gdb)
      * breakpoint.
      */
     copy_from_page(page, vaddr, &old_opcode, UPROBE_SWBP_INSN_SIZE);
     is_swbp = is_swbp_insn(&old_opcode);
 
     if (is_swbp_insn(new_opcode)) {
         if (is_swbp)        /* register: already installed? */
             return 0;
     } else {
         if (!is_swbp)       /* unregister: was it changed by us? */
             return 0;
     }
 
     return 1;
 }
 
 static struct delayed_uprobe *
 delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
 {
     struct delayed_uprobe *du;
 
     list_for_each_entry(du, &delayed_uprobe_list, list)
         if (du->uprobe == uprobe && du->mm == mm)
             return du;
     return NULL;
 }
 
 static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
 {
     struct delayed_uprobe *du;
 
     if (delayed_uprobe_check(uprobe, mm))
         return 0;
 
     du  = kzalloc(sizeof(*du), GFP_KERNEL);
     if (!du)
         return -ENOMEM;
 
     du->uprobe = uprobe;
     du->mm = mm;
     list_add(&du->list, &delayed_uprobe_list);
     return 0;
 }
 
 static void delayed_uprobe_delete(struct delayed_uprobe *du)
 {
     if (WARN_ON(!du))
         return;
     list_del(&du->list);
     kfree(du);
 }
 
 static void delayed_uprobe_remove(struct uprobe *uprobe, struct mm_struct *mm)
 {
     struct list_head *pos, *q;
     struct delayed_uprobe *du;
 
     if (!uprobe && !mm)
         return;
 
     list_for_each_safe(pos, q, &delayed_uprobe_list) {
         du = list_entry(pos, struct delayed_uprobe, list);
 
         if (uprobe && du->uprobe != uprobe)
             continue;
         if (mm && du->mm != mm)
             continue;
 
         delayed_uprobe_delete(du);
     }
 }
 
 static bool valid_ref_ctr_vma(struct uprobe *uprobe,
                   struct vm_area_struct *vma)
 {
     unsigned long vaddr = offset_to_vaddr(vma, uprobe->ref_ctr_offset);
 
     return uprobe->ref_ctr_offset &&
         vma->vm_file &&
         file_inode(vma->vm_file) == uprobe->inode &&
         (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
         vma->vm_start <= vaddr &&
         vma->vm_end > vaddr;
 }
 
 static struct vm_area_struct *
 find_ref_ctr_vma(struct uprobe *uprobe, struct mm_struct *mm)
 {
     struct vm_area_struct *tmp;
 
     for (tmp = mm->mmap; tmp; tmp = tmp->vm_next)
         if (valid_ref_ctr_vma(uprobe, tmp))
             return tmp;
 
     return NULL;
 }
 
 static int
 __update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
 {
     void *kaddr;
     struct page *page;
     struct vm_area_struct *vma;
     int ret;
     short *ptr;
 
     if (!vaddr || !d)
         return -EINVAL;
 
     ret = get_user_pages_remote(mm, vaddr, 1,
             FOLL_WRITE, &page, &vma, NULL);
     if (unlikely(ret <= 0)) {
         /*
          * We are asking for 1 page. If get_user_pages_remote() fails,
          * it may return 0, in that case we have to return error.
          */
         return ret == 0 ? -EBUSY : ret;
     }
 
     kaddr = kmap_atomic(page);
     ptr = kaddr + (vaddr & ~PAGE_MASK);
 
     if (unlikely(*ptr + d < 0)) {
         pr_warn("ref_ctr going negative. vaddr: 0x%lx, "
             "curr val: %d, delta: %d\n", vaddr, *ptr, d);
         ret = -EINVAL;
         goto out;
     }
 
     *ptr += d;
     ret = 0;
 out:
     kunmap_atomic(kaddr);
     put_page(page);
     return ret;
 }
 
 static void update_ref_ctr_warn(struct uprobe *uprobe,
                 struct mm_struct *mm, short d)
 {
     pr_warn("ref_ctr %s failed for inode: 0x%lx offset: "
         "0x%llx ref_ctr_offset: 0x%llx of mm: 0x%pK\n",
         d > 0 ? "increment" : "decrement", uprobe->inode->i_ino,
         (unsigned long long) uprobe->offset,
         (unsigned long long) uprobe->ref_ctr_offset, mm);
 }
 
 static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
               short d)
 {
     struct vm_area_struct *rc_vma;
     unsigned long rc_vaddr;
     int ret = 0;
 
     rc_vma = find_ref_ctr_vma(uprobe, mm);
 
     if (rc_vma) {
         rc_vaddr = offset_to_vaddr(rc_vma, uprobe->ref_ctr_offset);
         ret = __update_ref_ctr(mm, rc_vaddr, d);
         if (ret)
             update_ref_ctr_warn(uprobe, mm, d);
 
         if (d > 0)
             return ret;
     }
 
     mutex_lock(&delayed_uprobe_lock);
     if (d > 0)
         ret = delayed_uprobe_add(uprobe, mm);
     else
         delayed_uprobe_remove(uprobe, mm);
     mutex_unlock(&delayed_uprobe_lock);
 
     return ret;
 }
 
 /*
  * NOTE:
  * Expect the breakpoint instruction to be the smallest size instruction for
  * the architecture. If an arch has variable length instruction and the
  * breakpoint instruction is not of the smallest length instruction
  * supported by that architecture then we need to modify is_trap_at_addr and
  * uprobe_write_opcode accordingly. This would never be a problem for archs
  * that have fixed length instructions.
  *
  * uprobe_write_opcode - write the opcode at a given virtual address.
  * @auprobe: arch specific probepoint information.
  * @mm: the probed process address space.
  * @vaddr: the virtual address to store the opcode.
  * @opcode: opcode to be written at @vaddr.
  *
  * Called with mm->mmap_lock held for write.
  * Return 0 (success) or a negative errno.
  */
 int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
             unsigned long vaddr, uprobe_opcode_t opcode)
 {
     struct uprobe *uprobe;
     struct page *old_page, *new_page;
     struct vm_area_struct *vma;
     int ret, is_register, ref_ctr_updated = 0;
     bool orig_page_huge = false;
     unsigned int gup_flags = FOLL_FORCE;
 
     is_register = is_swbp_insn(&opcode);
     uprobe = container_of(auprobe, struct uprobe, arch);
 
 retry:
     if (is_register)
         gup_flags |= FOLL_SPLIT_PMD;
     /* Read the page with vaddr into memory */
     ret = get_user_pages_remote(mm, vaddr, 1, gup_flags,
                     &old_page, &vma, NULL);
     if (ret <= 0)
         return ret;
 
     ret = verify_opcode(old_page, vaddr, &opcode);
     if (ret <= 0)
         goto put_old;
 
     if (WARN(!is_register && PageCompound(old_page),
          "uprobe unregister should never work on compound page\n")) {
         ret = -EINVAL;
         goto put_old;
     }
 
     /* We are going to replace instruction, update ref_ctr. */
     if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
         ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);
         if (ret)
             goto put_old;
 
         ref_ctr_updated = 1;
     }
 
     ret = 0;
     if (!is_register && !PageAnon(old_page))
         goto put_old;
 
     ret = anon_vma_prepare(vma);
     if (ret)
         goto put_old;
 
     ret = -ENOMEM;
     new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
     if (!new_page)
         goto put_old;
 
     __SetPageUptodate(new_page);
     copy_highpage(new_page, old_page);
     copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
 
     if (!is_register) {
         struct page *orig_page;
         pgoff_t index;
 
         VM_BUG_ON_PAGE(!PageAnon(old_page), old_page);
 
         index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
         orig_page = find_get_page(vma->vm_file->f_inode->i_mapping,
                       index);
 
         if (orig_page) {
             if (PageUptodate(orig_page) &&
                 pages_identical(new_page, orig_page)) {
                 /* let go new_page */
                 put_page(new_page);
                 new_page = NULL;
 
                 if (PageCompound(orig_page))
                     orig_page_huge = true;
             }
             put_page(orig_page);
         }
     }
 
     ret = __replace_page(vma, vaddr, old_page, new_page);
     if (new_page)
         put_page(new_page);
 put_old:
     put_page(old_page);
 
     if (unlikely(ret == -EAGAIN))
         goto retry;
 
     /* Revert back reference counter if instruction update failed. */
     if (ret && is_register && ref_ctr_updated)
         update_ref_ctr(uprobe, mm, -1);
 
     /* try collapse pmd for compound page */
     if (!ret && orig_page_huge)
         collapse_pte_mapped_thp(mm, vaddr);
 
     return ret;
 }
 
 /**
  * set_swbp - store breakpoint at a given address.
  * @auprobe: arch specific probepoint information.
  * @mm: the probed process address space.
  * @vaddr: the virtual address to insert the opcode.
  *
  * For mm @mm, store the breakpoint instruction at @vaddr.
  * Return 0 (success) or a negative errno.
  */
 int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
     return uprobe_write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
 }
 
 /**
  * set_orig_insn - Restore the original instruction.
  * @mm: the probed process address space.
  * @auprobe: arch specific probepoint information.
  * @vaddr: the virtual address to insert the opcode.
  *
  * For mm @mm, restore the original opcode (opcode) at @vaddr.
  * Return 0 (success) or a negative errno.
  */
 int __weak
 set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
     return uprobe_write_opcode(auprobe, mm, vaddr,
             *(uprobe_opcode_t *)&auprobe->insn);
 }
 
 static struct uprobe *get_uprobe(struct uprobe *uprobe)
 {
     refcount_inc(&uprobe->ref);
     return uprobe;
 }
 
 static void put_uprobe(struct uprobe *uprobe)
 {
     if (refcount_dec_and_test(&uprobe->ref)) {
         /*
          * If application munmap(exec_vma) before uprobe_unregister()
          * gets called, we don't get a chance to remove uprobe from
          * delayed_uprobe_list from remove_breakpoint(). Do it here.
          */
         mutex_lock(&delayed_uprobe_lock);
         delayed_uprobe_remove(uprobe, NULL);
         mutex_unlock(&delayed_uprobe_lock);
         kfree(uprobe);
     }
 }
 
 static __always_inline
 int uprobe_cmp(const struct inode *l_inode, const loff_t l_offset,
            const struct uprobe *r)
 {
     if (l_inode < r->inode)
         return -1;
 
     if (l_inode > r->inode)
         return 1;
 
     if (l_offset < r->offset)
         return -1;
 
     if (l_offset > r->offset)
         return 1;
 
     return 0;
 }
 
 #define __node_2_uprobe(node) \
     rb_entry((node), struct uprobe, rb_node)
 
 struct __uprobe_key {
     struct inode *inode;
     loff_t offset;
 };
 
 static inline int __uprobe_cmp_key(const void *key, const struct rb_node *b)
 {
     const struct __uprobe_key *a = key;
     return uprobe_cmp(a->inode, a->offset, __node_2_uprobe(b));
 }
 
 static inline int __uprobe_cmp(struct rb_node *a, const struct rb_node *b)
 {
     struct uprobe *u = __node_2_uprobe(a);
     return uprobe_cmp(u->inode, u->offset, __node_2_uprobe(b));
 }
 
 static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset)
 {
     struct __uprobe_key key = {
         .inode = inode,
         .offset = offset,
     };
     struct rb_node *node = rb_find(&key, &uprobes_tree, __uprobe_cmp_key);
 
     if (node)
         return get_uprobe(__node_2_uprobe(node));
 
     return NULL;
 }
 
 /*
  * Find a uprobe corresponding to a given inode:offset
  * Acquires uprobes_treelock
  */
 static struct uprobe *find_uprobe(struct inode *inode, loff_t offset)
 {
     struct uprobe *uprobe;
 
     spin_lock(&uprobes_treelock);
     uprobe = __find_uprobe(inode, offset);
     spin_unlock(&uprobes_treelock);
 
     return uprobe;
 }
 
 static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
 {
     struct rb_node *node;
 
     node = rb_find_add(&uprobe->rb_node, &uprobes_tree, __uprobe_cmp);
     if (node)
         return get_uprobe(__node_2_uprobe(node));
 
     /* get access + creation ref */
     refcount_set(&uprobe->ref, 2);
     return NULL;
 }
 
 /*
  * Acquire uprobes_treelock.
  * Matching uprobe already exists in rbtree;
  *  increment (access refcount) and return the matching uprobe.
  *
  * No matching uprobe; insert the uprobe in rb_tree;
  *  get a double refcount (access + creation) and return NULL.
  */
 static struct uprobe *insert_uprobe(struct uprobe *uprobe)
 {
     struct uprobe *u;
 
     spin_lock(&uprobes_treelock);
     u = __insert_uprobe(uprobe);
     spin_unlock(&uprobes_treelock);
 
     return u;
 }
 
 static void
 ref_ctr_mismatch_warn(struct uprobe *cur_uprobe, struct uprobe *uprobe)
 {
     pr_warn("ref_ctr_offset mismatch. inode: 0x%lx offset: 0x%llx "
         "ref_ctr_offset(old): 0x%llx ref_ctr_offset(new): 0x%llx\n",
         uprobe->inode->i_ino, (unsigned long long) uprobe->offset,
         (unsigned long long) cur_uprobe->ref_ctr_offset,
         (unsigned long long) uprobe->ref_ctr_offset);
 }
 
 static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
                    loff_t ref_ctr_offset)
 {
     struct uprobe *uprobe, *cur_uprobe;
 
     uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
     if (!uprobe)
         return NULL;
 
     uprobe->inode = inode;
     uprobe->offset = offset;
     uprobe->ref_ctr_offset = ref_ctr_offset;
     init_rwsem(&uprobe->register_rwsem);
     init_rwsem(&uprobe->consumer_rwsem);
 
     /* add to uprobes_tree, sorted on inode:offset */
     cur_uprobe = insert_uprobe(uprobe);
     /* a uprobe exists for this inode:offset combination */
     if (cur_uprobe) {
         if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
             ref_ctr_mismatch_warn(cur_uprobe, uprobe);
             put_uprobe(cur_uprobe);
             kfree(uprobe);
             return ERR_PTR(-EINVAL);
         }
         kfree(uprobe);
         uprobe = cur_uprobe;
     }
 
     return uprobe;
 }
 
 static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
     down_write(&uprobe->consumer_rwsem);
     uc->next = uprobe->consumers;
     uprobe->consumers = uc;
     up_write(&uprobe->consumer_rwsem);
 }
 
 /*
  * For uprobe @uprobe, delete the consumer @uc.
  * Return true if the @uc is deleted successfully
  * or return false.
  */
 static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
     struct uprobe_consumer **con;
     bool ret = false;
 
     down_write(&uprobe->consumer_rwsem);
     for (con = &uprobe->consumers; *con; con = &(*con)->next) {
         if (*con == uc) {
             *con = uc->next;
             ret = true;
             break;
         }
     }
     up_write(&uprobe->consumer_rwsem);
 
     return ret;
 }
 
 static int __copy_insn(struct address_space *mapping, struct file *filp,
             void *insn, int nbytes, loff_t offset)
 {
     struct page *page;
     /*
      * Ensure that the page that has the original instruction is populated
      * and in page-cache. If ->read_folio == NULL it must be shmem_mapping(),
      * see uprobe_register().
      */
     if (mapping->a_ops->read_folio)
         page = read_mapping_page(mapping, offset >> PAGE_SHIFT, filp);
     else
         page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
     if (IS_ERR(page))
         return PTR_ERR(page);
 
     copy_from_page(page, offset, insn, nbytes);
     put_page(page);
 
     return 0;
 }
 
 static int copy_insn(struct uprobe *uprobe, struct file *filp)
 {
     struct address_space *mapping = uprobe->inode->i_mapping;
     loff_t offs = uprobe->offset;
     void *insn = &uprobe->arch.insn;
     int size = sizeof(uprobe->arch.insn);
     int len, err = -EIO;
 
     /* Copy only available bytes, -EIO if nothing was read */
     do {
         if (offs >= i_size_read(uprobe->inode))
             break;
 
         len = min_t(int, size, PAGE_SIZE - (offs & ~PAGE_MASK));
         err = __copy_insn(mapping, filp, insn, len, offs);
         if (err)
             break;
 
         insn += len;
         offs += len;
         size -= len;
     } while (size);
 
     return err;
 }
 
 static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
                 struct mm_struct *mm, unsigned long vaddr)
 {
     int ret = 0;
 
     if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
         return ret;
 
     /* TODO: move this into _register, until then we abuse this sem. */
     down_write(&uprobe->consumer_rwsem);
     if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
         goto out;
 
     ret = copy_insn(uprobe, file);
     if (ret)
         goto out;
 
     ret = -ENOTSUPP;
     if (is_trap_insn((uprobe_opcode_t *)&uprobe->arch.insn))
         goto out;
 
     ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, vaddr);
     if (ret)
         goto out;
 
     smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */
     set_bit(UPROBE_COPY_INSN, &uprobe->flags);
 
  out:
     up_write(&uprobe->consumer_rwsem);
 
     return ret;
 }
 
 static inline bool consumer_filter(struct uprobe_consumer *uc,
                    enum uprobe_filter_ctx ctx, struct mm_struct *mm)
 {
     return !uc->filter || uc->filter(uc, ctx, mm);
 }
 
 static bool filter_chain(struct uprobe *uprobe,
              enum uprobe_filter_ctx ctx, struct mm_struct *mm)
 {
     struct uprobe_consumer *uc;
     bool ret = false;
 
     down_read(&uprobe->consumer_rwsem);
     for (uc = uprobe->consumers; uc; uc = uc->next) {
         ret = consumer_filter(uc, ctx, mm);
         if (ret)
             break;
     }
     up_read(&uprobe->consumer_rwsem);
 
     return ret;
 }
 
 static int
 install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
             struct vm_area_struct *vma, unsigned long vaddr)
 {
     bool first_uprobe;
     int ret;
 
     ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
     if (ret)
         return ret;
 
     /*
      * set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
      * the task can hit this breakpoint right after __replace_page().
      */
     first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags);
     if (first_uprobe)
         set_bit(MMF_HAS_UPROBES, &mm->flags);
 
     ret = set_swbp(&uprobe->arch, mm, vaddr);
     if (!ret)
         clear_bit(MMF_RECALC_UPROBES, &mm->flags);
     else if (first_uprobe)
         clear_bit(MMF_HAS_UPROBES, &mm->flags);
 
     return ret;
 }
 
 static int
 remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
 {
     set_bit(MMF_RECALC_UPROBES, &mm->flags);
     return set_orig_insn(&uprobe->arch, mm, vaddr);
 }
 
 static inline bool uprobe_is_active(struct uprobe *uprobe)
 {
     return !RB_EMPTY_NODE(&uprobe->rb_node);
 }
 /*
  * There could be threads that have already hit the breakpoint. They
  * will recheck the current insn and restart if find_uprobe() fails.
  * See find_active_uprobe().
  */
 static void delete_uprobe(struct uprobe *uprobe)
 {
     if (WARN_ON(!uprobe_is_active(uprobe)))
         return;
 
     spin_lock(&uprobes_treelock);
     rb_erase(&uprobe->rb_node, &uprobes_tree);
     spin_unlock(&uprobes_treelock);
     RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
     put_uprobe(uprobe);
 }
 
 struct map_info {
     struct map_info *next;
     struct mm_struct *mm;
     unsigned long vaddr;
 };
 
 static inline struct map_info *free_map_info(struct map_info *info)
 {
     struct map_info *next = info->next;
     kfree(info);
     return next;
 }
 
 static struct map_info *
 build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
 {
     unsigned long pgoff = offset >> PAGE_SHIFT;
     struct vm_area_struct *vma;
     struct map_info *curr = NULL;
     struct map_info *prev = NULL;
     struct map_info *info;
     int more = 0;
 
  again:
     i_mmap_lock_read(mapping);
     vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
         if (!valid_vma(vma, is_register))
             continue;
 
         if (!prev && !more) {
             /*
              * Needs GFP_NOWAIT to avoid i_mmap_rwsem recursion through
              * reclaim. This is optimistic, no harm done if it fails.
              */
             prev = kmalloc(sizeof(struct map_info),
                     GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
             if (prev)
                 prev->next = NULL;
         }
         if (!prev) {
             more++;
             continue;
         }
 
         if (!mmget_not_zero(vma->vm_mm))
             continue;
 
         info = prev;
         prev = prev->next;
         info->next = curr;
         curr = info;
 
         info->mm = vma->vm_mm;
         info->vaddr = offset_to_vaddr(vma, offset);
     }
     i_mmap_unlock_read(mapping);
 
     if (!more)
         goto out;
 
     prev = curr;
     while (curr) {
         mmput(curr->mm);
         curr = curr->next;
     }
 
     do {
         info = kmalloc(sizeof(struct map_info), GFP_KERNEL);
         if (!info) {
             curr = ERR_PTR(-ENOMEM);
             goto out;
         }
         info->next = prev;
         prev = info;
     } while (--more);
 
     goto again;
  out:
     while (prev)
         prev = free_map_info(prev);
     return curr;
 }
 
 static int
 register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
 {
     bool is_register = !!new;
     struct map_info *info;
     int err = 0;
 
     percpu_down_write(&dup_mmap_sem);
     info = build_map_info(uprobe->inode->i_mapping,
                     uprobe->offset, is_register);
     if (IS_ERR(info)) {
         err = PTR_ERR(info);
         goto out;
     }
 
     while (info) {
         struct mm_struct *mm = info->mm;
         struct vm_area_struct *vma;
 
         if (err && is_register)
             goto free;
 
         mmap_write_lock(mm);
         vma = find_vma(mm, info->vaddr);
         if (!vma || !valid_vma(vma, is_register) ||
             file_inode(vma->vm_file) != uprobe->inode)
             goto unlock;
 
         if (vma->vm_start > info->vaddr ||
             vaddr_to_offset(vma, info->vaddr) != uprobe->offset)
             goto unlock;
 
         if (is_register) {
             /* consult only the "caller", new consumer. */
             if (consumer_filter(new,
                     UPROBE_FILTER_REGISTER, mm))
                 err = install_breakpoint(uprobe, mm, vma, info->vaddr);
         } else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
             if (!filter_chain(uprobe,
                     UPROBE_FILTER_UNREGISTER, mm))
                 err |= remove_breakpoint(uprobe, mm, info->vaddr);
         }
 
  unlock:
         mmap_write_unlock(mm);
  free:
         mmput(mm);
         info = free_map_info(info);
     }
  out:
     percpu_up_write(&dup_mmap_sem);
     return err;
 }
 
 static void
 __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
     int err;
 
     if (WARN_ON(!consumer_del(uprobe, uc)))
         return;
 
     err = register_for_each_vma(uprobe, NULL);
     /* TODO : cant unregister? schedule a worker thread */
     if (!uprobe->consumers && !err)
         delete_uprobe(uprobe);
 }
 
 /*
  * uprobe_unregister - unregister an already registered probe.
  * @inode: the file in which the probe has to be removed.
  * @offset: offset from the start of the file.
  * @uc: identify which probe if multiple probes are colocated.
  */
 void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
 {
     struct uprobe *uprobe;
 
     uprobe = find_uprobe(inode, offset);
     if (WARN_ON(!uprobe))
         return;
 
     down_write(&uprobe->register_rwsem);
     __uprobe_unregister(uprobe, uc);
     up_write(&uprobe->register_rwsem);
     put_uprobe(uprobe);
 }
 EXPORT_SYMBOL_GPL(uprobe_unregister);
 
 /*
  * __uprobe_register - register a probe
  * @inode: the file in which the probe has to be placed.
  * @offset: offset from the start of the file.
  * @uc: information on howto handle the probe..
  *
  * Apart from the access refcount, __uprobe_register() takes a creation
  * refcount (thro alloc_uprobe) if and only if this @uprobe is getting
  * inserted into the rbtree (i.e first consumer for a @inode:@offset
  * tuple).  Creation refcount stops uprobe_unregister from freeing the
  * @uprobe even before the register operation is complete. Creation
  * refcount is released when the last @uc for the @uprobe
  * unregisters. Caller of __uprobe_register() is required to keep @inode
  * (and the containing mount) referenced.
  *
  * Return errno if it cannot successully install probes
  * else return 0 (success)
  */
 static int __uprobe_register(struct inode *inode, loff_t offset,
                  loff_t ref_ctr_offset, struct uprobe_consumer *uc)
 {
     struct uprobe *uprobe;
     int ret;
 
     /* Uprobe must have at least one set consumer */
     if (!uc->handler && !uc->ret_handler)
         return -EINVAL;
 
     /* copy_insn() uses read_mapping_page() or shmem_read_mapping_page() */
     if (!inode->i_mapping->a_ops->read_folio &&
         !shmem_mapping(inode->i_mapping))
         return -EIO;
     /* Racy, just to catch the obvious mistakes */
     if (offset > i_size_read(inode))
         return -EINVAL;
 
     /*
      * This ensures that copy_from_page(), copy_to_page() and
      * __update_ref_ctr() can't cross page boundary.
      */
     if (!IS_ALIGNED(offset, UPROBE_SWBP_INSN_SIZE))
         return -EINVAL;
     if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
         return -EINVAL;
 
  retry:
     uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
     if (!uprobe)
         return -ENOMEM;
     if (IS_ERR(uprobe))
         return PTR_ERR(uprobe);
 
     /*
      * We can race with uprobe_unregister()->delete_uprobe().
      * Check uprobe_is_active() and retry if it is false.
      */
     down_write(&uprobe->register_rwsem);
     ret = -EAGAIN;
     if (likely(uprobe_is_active(uprobe))) {
         consumer_add(uprobe, uc);
         ret = register_for_each_vma(uprobe, uc);
         if (ret)
             __uprobe_unregister(uprobe, uc);
     }
     up_write(&uprobe->register_rwsem);
     put_uprobe(uprobe);
 
     if (unlikely(ret == -EAGAIN))
         goto retry;
     return ret;
 }
 
 int uprobe_register(struct inode *inode, loff_t offset,
             struct uprobe_consumer *uc)
 {
     return __uprobe_register(inode, offset, 0, uc);
 }
 EXPORT_SYMBOL_GPL(uprobe_register);
 
 int uprobe_register_refctr(struct inode *inode, loff_t offset,
                loff_t ref_ctr_offset, struct uprobe_consumer *uc)
 {
     return __uprobe_register(inode, offset, ref_ctr_offset, uc);
 }
 EXPORT_SYMBOL_GPL(uprobe_register_refctr);
 
 /*
  * uprobe_apply - unregister an already registered probe.
  * @inode: the file in which the probe has to be removed.
  * @offset: offset from the start of the file.
  * @uc: consumer which wants to add more or remove some breakpoints
  * @add: add or remove the breakpoints
  */
 int uprobe_apply(struct inode *inode, loff_t offset,
             struct uprobe_consumer *uc, bool add)
 {
     struct uprobe *uprobe;
     struct uprobe_consumer *con;
     int ret = -ENOENT;
 
     uprobe = find_uprobe(inode, offset);
     if (WARN_ON(!uprobe))
         return ret;
 
     down_write(&uprobe->register_rwsem);
     for (con = uprobe->consumers; con && con != uc ; con = con->next)
         ;
     if (con)
         ret = register_for_each_vma(uprobe, add ? uc : NULL);
     up_write(&uprobe->register_rwsem);
     put_uprobe(uprobe);
 
     return ret;
 }
 
 static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
 {
     struct vm_area_struct *vma;
     int err = 0;
 
     mmap_read_lock(mm);
     for (vma = mm->mmap; vma; vma = vma->vm_next) {
         unsigned long vaddr;
         loff_t offset;
 
         if (!valid_vma(vma, false) ||
             file_inode(vma->vm_file) != uprobe->inode)
             continue;
 
         offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
         if (uprobe->offset <  offset ||
             uprobe->offset >= offset + vma->vm_end - vma->vm_start)
             continue;
 
         vaddr = offset_to_vaddr(vma, uprobe->offset);
         err |= remove_breakpoint(uprobe, mm, vaddr);
     }
     mmap_read_unlock(mm);
 
     return err;
 }
 
 static struct rb_node *
 find_node_in_range(struct inode *inode, loff_t min, loff_t max)
 {
     struct rb_node *n = uprobes_tree.rb_node;
 
     while (n) {
         struct uprobe *u = rb_entry(n, struct uprobe, rb_node);
 
         if (inode < u->inode) {
             n = n->rb_left;
         } else if (inode > u->inode) {
             n = n->rb_right;
         } else {
             if (max < u->offset)
                 n = n->rb_left;
             else if (min > u->offset)
                 n = n->rb_right;
             else
                 break;
         }
     }
 
     return n;
 }
 
 /*
  * For a given range in vma, build a list of probes that need to be inserted.
  */
 static void build_probe_list(struct inode *inode,
                 struct vm_area_struct *vma,
                 unsigned long start, unsigned long end,
                 struct list_head *head)
 {
     loff_t min, max;
     struct rb_node *n, *t;
     struct uprobe *u;
 
     INIT_LIST_HEAD(head);
     min = vaddr_to_offset(vma, start);
     max = min + (end - start) - 1;
 
     spin_lock(&uprobes_treelock);
     n = find_node_in_range(inode, min, max);
     if (n) {
         for (t = n; t; t = rb_prev(t)) {
             u = rb_entry(t, struct uprobe, rb_node);
             if (u->inode != inode || u->offset < min)
                 break;
             list_add(&u->pending_list, head);
             get_uprobe(u);
         }
         for (t = n; (t = rb_next(t)); ) {
             u = rb_entry(t, struct uprobe, rb_node);
             if (u->inode != inode || u->offset > max)
                 break;
             list_add(&u->pending_list, head);
             get_uprobe(u);
         }
     }
     spin_unlock(&uprobes_treelock);
 }
 
 /* @vma contains reference counter, not the probed instruction. */
 static int delayed_ref_ctr_inc(struct vm_area_struct *vma)
 {
     struct list_head *pos, *q;
     struct delayed_uprobe *du;
     unsigned long vaddr;
     int ret = 0, err = 0;
 
     mutex_lock(&delayed_uprobe_lock);
     list_for_each_safe(pos, q, &delayed_uprobe_list) {
         du = list_entry(pos, struct delayed_uprobe, list);
 
         if (du->mm != vma->vm_mm ||
             !valid_ref_ctr_vma(du->uprobe, vma))
             continue;
 
         vaddr = offset_to_vaddr(vma, du->uprobe->ref_ctr_offset);
         ret = __update_ref_ctr(vma->vm_mm, vaddr, 1);
         if (ret) {
             update_ref_ctr_warn(du->uprobe, vma->vm_mm, 1);
             if (!err)
                 err = ret;
         }
         delayed_uprobe_delete(du);
     }
     mutex_unlock(&delayed_uprobe_lock);
     return err;
 }
 
 /*
  * Called from mmap_region/vma_adjust with mm->mmap_lock acquired.
  *
  * Currently we ignore all errors and always return 0, the callers
  * can't handle the failure anyway.
  */
 int uprobe_mmap(struct vm_area_struct *vma)
 {
     struct list_head tmp_list;
     struct uprobe *uprobe, *u;
     struct inode *inode;
 
     if (no_uprobe_events())
         return 0;
 
     if (vma->vm_file &&
         (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
         test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
         delayed_ref_ctr_inc(vma);
 
     if (!valid_vma(vma, true))
         return 0;
 
     inode = file_inode(vma->vm_file);
     if (!inode)
         return 0;
 
     mutex_lock(uprobes_mmap_hash(inode));
     build_probe_list(inode, vma, vma->vm_start, vma->vm_end, &tmp_list);
     /*
      * We can race with uprobe_unregister(), this uprobe can be already
      * removed. But in this case filter_chain() must return false, all
      * consumers have gone away.
      */
     list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
         if (!fatal_signal_pending(current) &&
             filter_chain(uprobe, UPROBE_FILTER_MMAP, vma->vm_mm)) {
             unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
             install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
         }
         put_uprobe(uprobe);
     }
     mutex_unlock(uprobes_mmap_hash(inode));
 
     return 0;
 }
 
 static bool
 vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
     loff_t min, max;
     struct inode *inode;
     struct rb_node *n;
 
     inode = file_inode(vma->vm_file);
 
     min = vaddr_to_offset(vma, start);
     max = min + (end - start) - 1;
 
     spin_lock(&uprobes_treelock);
     n = find_node_in_range(inode, min, max);
     spin_unlock(&uprobes_treelock);
 
     return !!n;
 }
 
 /*
  * Called in context of a munmap of a vma.
  */
 void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
     if (no_uprobe_events() || !valid_vma(vma, false))
         return;
 
     if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
         return;
 
     if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) ||
          test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags))
         return;
 
     if (vma_has_uprobes(vma, start, end))
         set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags);
 }
 
 /* Slot allocation for XOL */
 static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
 {
     struct vm_area_struct *vma;
     int ret;
 
     if (mmap_write_lock_killable(mm))
         return -EINTR;
 
     if (mm->uprobes_state.xol_area) {
         ret = -EALREADY;
         goto fail;
     }
 
     if (!area->vaddr) {
         /* Try to map as high as possible, this is only a hint. */
         area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
                         PAGE_SIZE, 0, 0);
         if (IS_ERR_VALUE(area->vaddr)) {
             ret = area->vaddr;
             goto fail;
         }
     }
 
     vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE,
                 VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO,
                 &area->xol_mapping);
     if (IS_ERR(vma)) {
         ret = PTR_ERR(vma);
         goto fail;
     }
 
     ret = 0;
     /* pairs with get_xol_area() */
     smp_store_release(&mm->uprobes_state.xol_area, area); /* ^^^ */
  fail:
     mmap_write_unlock(mm);
 
     return ret;
 }
 
 static struct xol_area *__create_xol_area(unsigned long vaddr)
 {
     struct mm_struct *mm = current->mm;
     uprobe_opcode_t insn = UPROBE_SWBP_INSN;
     struct xol_area *area;
 
     area = kmalloc(sizeof(*area), GFP_KERNEL);
     if (unlikely(!area))
         goto out;
 
     area->bitmap = kcalloc(BITS_TO_LONGS(UINSNS_PER_PAGE), sizeof(long),
                    GFP_KERNEL);
     if (!area->bitmap)
         goto free_area;
 
     area->xol_mapping.name = "[uprobes]";
     area->xol_mapping.fault = NULL;
     area->xol_mapping.pages = area->pages;
     area->pages[0] = alloc_page(GFP_HIGHUSER);
     if (!area->pages[0])
         goto free_bitmap;
     area->pages[1] = NULL;
 
     area->vaddr = vaddr;
     init_waitqueue_head(&area->wq);
     /* Reserve the 1st slot for get_trampoline_vaddr() */
     set_bit(0, area->bitmap);
     atomic_set(&area->slot_count, 1);
     arch_uprobe_copy_ixol(area->pages[0], 0, &insn, UPROBE_SWBP_INSN_SIZE);
 
     if (!xol_add_vma(mm, area))
         return area;
 
     __free_page(area->pages[0]);
  free_bitmap:
     kfree(area->bitmap);
  free_area:
     kfree(area);
  out:
     return NULL;
 }
 
 /*
  * get_xol_area - Allocate process's xol_area if necessary.
  * This area will be used for storing instructions for execution out of line.
  *
  * Returns the allocated area or NULL.
  */
 static struct xol_area *get_xol_area(void)
 {
     struct mm_struct *mm = current->mm;
     struct xol_area *area;
 
     if (!mm->uprobes_state.xol_area)
         __create_xol_area(0);
 
     /* Pairs with xol_add_vma() smp_store_release() */
     area = READ_ONCE(mm->uprobes_state.xol_area); /* ^^^ */
     return area;
 }
 
 /*
  * uprobe_clear_state - Free the area allocated for slots.
  */
 void uprobe_clear_state(struct mm_struct *mm)
 {
     struct xol_area *area = mm->uprobes_state.xol_area;
 
     mutex_lock(&delayed_uprobe_lock);
     delayed_uprobe_remove(NULL, mm);
     mutex_unlock(&delayed_uprobe_lock);
 
     if (!area)
         return;
 
     put_page(area->pages[0]);
     kfree(area->bitmap);
     kfree(area);
 }
 
 void uprobe_start_dup_mmap(void)
 {
     percpu_down_read(&dup_mmap_sem);
 }
 
 void uprobe_end_dup_mmap(void)
 {
     percpu_up_read(&dup_mmap_sem);
 }
 
 void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
 {
     if (test_bit(MMF_HAS_UPROBES, &oldmm->flags)) {
         set_bit(MMF_HAS_UPROBES, &newmm->flags);
         /* unconditionally, dup_mmap() skips VM_DONTCOPY vmas */
         set_bit(MMF_RECALC_UPROBES, &newmm->flags);
     }
 }
 
 /*
  *  - search for a free slot.
  */
 static unsigned long xol_take_insn_slot(struct xol_area *area)
 {
     unsigned long slot_addr;
     int slot_nr;
 
     do {
         slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
         if (slot_nr < UINSNS_PER_PAGE) {
             if (!test_and_set_bit(slot_nr, area->bitmap))
                 break;
 
             slot_nr = UINSNS_PER_PAGE;
             continue;
         }
         wait_event(area->wq, (atomic_read(&area->slot_count) < UINSNS_PER_PAGE));
     } while (slot_nr >= UINSNS_PER_PAGE);
 
     slot_addr = area->vaddr + (slot_nr * UPROBE_XOL_SLOT_BYTES);
     atomic_inc(&area->slot_count);
 
     return slot_addr;
 }
 
 /*
  * xol_get_insn_slot - allocate a slot for xol.
  * Returns the allocated slot address or 0.
  */
 static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 {
     struct xol_area *area;
     unsigned long xol_vaddr;
 
     area = get_xol_area();
     if (!area)
         return 0;
 
     xol_vaddr = xol_take_insn_slot(area);
     if (unlikely(!xol_vaddr))
         return 0;
 
     arch_uprobe_copy_ixol(area->pages[0], xol_vaddr,
                   &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
 
     return xol_vaddr;
 }
 
 /*
  * xol_free_insn_slot - If slot was earlier allocated by
  * @xol_get_insn_slot(), make the slot available for
  * subsequent requests.
  */
 static void xol_free_insn_slot(struct task_struct *tsk)
 {
     struct xol_area *area;
     unsigned long vma_end;
     unsigned long slot_addr;
 
     if (!tsk->mm || !tsk->mm->uprobes_state.xol_area || !tsk->utask)
         return;
 
     slot_addr = tsk->utask->xol_vaddr;
     if (unlikely(!slot_addr))
         return;
 
     area = tsk->mm->uprobes_state.xol_area;
     vma_end = area->vaddr + PAGE_SIZE;
     if (area->vaddr <= slot_addr && slot_addr < vma_end) {
         unsigned long offset;
         int slot_nr;
 
         offset = slot_addr - area->vaddr;
         slot_nr = offset / UPROBE_XOL_SLOT_BYTES;
         if (slot_nr >= UINSNS_PER_PAGE)
             return;
 
         clear_bit(slot_nr, area->bitmap);
         atomic_dec(&area->slot_count);
         smp_mb__after_atomic(); /* pairs with prepare_to_wait() */
         if (waitqueue_active(&area->wq))
             wake_up(&area->wq);
 
         tsk->utask->xol_vaddr = 0;
     }
 }
 
 void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
                   void *src, unsigned long len)
 {
     /* Initialize the slot */
     copy_to_page(page, vaddr, src, len);
 
     /*
      * We probably need flush_icache_user_page() but it needs vma.
      * This should work on most of architectures by default. If
      * architecture needs to do something different it can define
      * its own version of the function.
      */
     flush_dcache_page(page);
 }
 
 /**
  * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
  * @regs: Reflects the saved state of the task after it has hit a breakpoint
  * instruction.
  * Return the address of the breakpoint instruction.
  */
 unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs)
 {
     return instruction_pointer(regs) - UPROBE_SWBP_INSN_SIZE;
 }
 
 unsigned long uprobe_get_trap_addr(struct pt_regs *regs)
 {
     struct uprobe_task *utask = current->utask;
 
     if (unlikely(utask && utask->active_uprobe))
         return utask->vaddr;
 
     return instruction_pointer(regs);
 }
 
 static struct return_instance *free_ret_instance(struct return_instance *ri)
 {
     struct return_instance *next = ri->next;
     put_uprobe(ri->uprobe);
     kfree(ri);
     return next;
 }
 
 /*
  * Called with no locks held.
  * Called in context of an exiting or an exec-ing thread.
  */
 void uprobe_free_utask(struct task_struct *t)
 {
     struct uprobe_task *utask = t->utask;
     struct return_instance *ri;
 
     if (!utask)
         return;
 
     if (utask->active_uprobe)
         put_uprobe(utask->active_uprobe);
 
     ri = utask->return_instances;
     while (ri)
         ri = free_ret_instance(ri);
 
     xol_free_insn_slot(t);
     kfree(utask);
     t->utask = NULL;
 }
 
 /*
  * Allocate a uprobe_task object for the task if necessary.
  * Called when the thread hits a breakpoint.
  *
  * Returns:
  * - pointer to new uprobe_task on success
  * - NULL otherwise
  */
 static struct uprobe_task *get_utask(void)
 {
     if (!current->utask)
         current->utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
     return current->utask;
 }
 
 static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
 {
     struct uprobe_task *n_utask;
     struct return_instance **p, *o, *n;
 
     n_utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
     if (!n_utask)
         return -ENOMEM;
     t->utask = n_utask;
 
     p = &n_utask->return_instances;
     for (o = o_utask->return_instances; o; o = o->next) {
         n = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
         if (!n)
             return -ENOMEM;
 
         *n = *o;
         get_uprobe(n->uprobe);
         n->next = NULL;
 
         *p = n;
         p = &n->next;
         n_utask->depth++;
     }
 
     return 0;
 }
 
 static void uprobe_warn(struct task_struct *t, const char *msg)
 {
     pr_warn("uprobe: %s:%d failed to %s\n",
             current->comm, current->pid, msg);
 }
 
 static void dup_xol_work(struct callback_head *work)
 {
     if (current->flags & PF_EXITING)
         return;
 
     if (!__create_xol_area(current->utask->dup_xol_addr) &&
             !fatal_signal_pending(current))
         uprobe_warn(current, "dup xol area");
 }
 
 /*
  * Called in context of a new clone/fork from copy_process.
  */
 void uprobe_copy_process(struct task_struct *t, unsigned long flags)
 {
     struct uprobe_task *utask = current->utask;
     struct mm_struct *mm = current->mm;
     struct xol_area *area;
 
     t->utask = NULL;
 
     if (!utask || !utask->return_instances)
         return;
 
     if (mm == t->mm && !(flags & CLONE_VFORK))
         return;
 
     if (dup_utask(t, utask))
         return uprobe_warn(t, "dup ret instances");
 
     /* The task can fork() after dup_xol_work() fails */
     area = mm->uprobes_state.xol_area;
     if (!area)
         return uprobe_warn(t, "dup xol area");
 
     if (mm == t->mm)
         return;
 
     t->utask->dup_xol_addr = area->vaddr;
     init_task_work(&t->utask->dup_xol_work, dup_xol_work);
     task_work_add(t, &t->utask->dup_xol_work, TWA_RESUME);
 }
 
 /*
  * Current area->vaddr notion assume the trampoline address is always
  * equal area->vaddr.
  *
  * Returns -1 in case the xol_area is not allocated.
  */
 static unsigned long get_trampoline_vaddr(void)
 {
     struct xol_area *area;
     unsigned long trampoline_vaddr = -1;
 
     /* Pairs with xol_add_vma() smp_store_release() */
     area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */
     if (area)
         trampoline_vaddr = area->vaddr;
 
     return trampoline_vaddr;
 }
 
 static void cleanup_return_instances(struct uprobe_task *utask, bool chained,
                     struct pt_regs *regs)
 {
     struct return_instance *ri = utask->return_instances;
     enum rp_check ctx = chained ? RP_CHECK_CHAIN_CALL : RP_CHECK_CALL;
 
     while (ri && !arch_uretprobe_is_alive(ri, ctx, regs)) {
         ri = free_ret_instance(ri);
         utask->depth--;
     }
     utask->return_instances = ri;
 }
 
 static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
 {
     struct return_instance *ri;
     struct uprobe_task *utask;
     unsigned long orig_ret_vaddr, trampoline_vaddr;
     bool chained;
 
     if (!get_xol_area())
         return;
 
     utask = get_utask();
     if (!utask)
         return;
 
     if (utask->depth >= MAX_URETPROBE_DEPTH) {
         printk_ratelimited(KERN_INFO "uprobe: omit uretprobe due to"
                 " nestedness limit pid/tgid=%d/%d\n",
                 current->pid, current->tgid);
         return;
     }
 
     ri = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
     if (!ri)
         return;
 
     trampoline_vaddr = get_trampoline_vaddr();
     orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
     if (orig_ret_vaddr == -1)
         goto fail;
 
     /* drop the entries invalidated by longjmp() */
     chained = (orig_ret_vaddr == trampoline_vaddr);
     cleanup_return_instances(utask, chained, regs);
 
     /*
      * We don't want to keep trampoline address in stack, rather keep the
      * original return address of first caller thru all the consequent
      * instances. This also makes breakpoint unwrapping easier.
      */
     if (chained) {
         if (!utask->return_instances) {
             /*
              * This situation is not possible. Likely we have an
              * attack from user-space.
              */
             uprobe_warn(current, "handle tail call");
             goto fail;
         }
         orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
     }
 
     ri->uprobe = get_uprobe(uprobe);
     ri->func = instruction_pointer(regs);
     ri->stack = user_stack_pointer(regs);
     ri->orig_ret_vaddr = orig_ret_vaddr;
     ri->chained = chained;
 
     utask->depth++;
     ri->next = utask->return_instances;
     utask->return_instances = ri;
 
     return;
  fail:
     kfree(ri);
 }
 
 /* Prepare to single-step probed instruction out of line. */
 static int
 pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
 {
     struct uprobe_task *utask;
     unsigned long xol_vaddr;
     int err;
 
     utask = get_utask();
     if (!utask)
         return -ENOMEM;
 
     xol_vaddr = xol_get_insn_slot(uprobe);
     if (!xol_vaddr)
         return -ENOMEM;
 
     utask->xol_vaddr = xol_vaddr;
     utask->vaddr = bp_vaddr;
 
     err = arch_uprobe_pre_xol(&uprobe->arch, regs);
     if (unlikely(err)) {
         xol_free_insn_slot(current);
         return err;
     }
 
     utask->active_uprobe = uprobe;
     utask->state = UTASK_SSTEP;
     return 0;
 }
 
 /*
  * If we are singlestepping, then ensure this thread is not connected to
  * non-fatal signals until completion of singlestep.  When xol insn itself
  * triggers the signal,  restart the original insn even if the task is
  * already SIGKILL'ed (since coredump should report the correct ip).  This
  * is even more important if the task has a handler for SIGSEGV/etc, The
  * _same_ instruction should be repeated again after return from the signal
  * handler, and SSTEP can never finish in this case.
  */
 bool uprobe_deny_signal(void)
 {
     struct task_struct *t = current;
     struct uprobe_task *utask = t->utask;
 
     if (likely(!utask || !utask->active_uprobe))
         return false;
 
     WARN_ON_ONCE(utask->state != UTASK_SSTEP);
 
     if (task_sigpending(t)) {
         spin_lock_irq(&t->sighand->siglock);
         clear_tsk_thread_flag(t, TIF_SIGPENDING);
         spin_unlock_irq(&t->sighand->siglock);
 
         if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
             utask->state = UTASK_SSTEP_TRAPPED;
             set_tsk_thread_flag(t, TIF_UPROBE);
         }
     }
 
     return true;
 }
 
 static void mmf_recalc_uprobes(struct mm_struct *mm)
 {
     struct vm_area_struct *vma;
 
     for (vma = mm->mmap; vma; vma = vma->vm_next) {
         if (!valid_vma(vma, false))
             continue;
         /*
          * This is not strictly accurate, we can race with
          * uprobe_unregister() and see the already removed
          * uprobe if delete_uprobe() was not yet called.
          * Or this uprobe can be filtered out.
          */
         if (vma_has_uprobes(vma, vma->vm_start, vma->vm_end))
             return;
     }
 
     clear_bit(MMF_HAS_UPROBES, &mm->flags);
 }
 
 static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
 {
     struct page *page;
     uprobe_opcode_t opcode;
     int result;
 
     if (WARN_ON_ONCE(!IS_ALIGNED(vaddr, UPROBE_SWBP_INSN_SIZE)))
         return -EINVAL;
 
     pagefault_disable();
     result = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
     pagefault_enable();
 
     if (likely(result == 0))
         goto out;
 
     /*
      * The NULL 'tsk' here ensures that any faults that occur here
      * will not be accounted to the task.  'mm' *is* current->mm,
      * but we treat this as a 'remote' access since it is
      * essentially a kernel access to the memory.
      */
     result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page,
             NULL, NULL);
     if (result < 0)
         return result;
 
     copy_from_page(page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
     put_page(page);
  out:
     /* This needs to return true for any variant of the trap insn */
     return is_trap_insn(&opcode);
 }
 
 static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
 {
     struct mm_struct *mm = current->mm;
     struct uprobe *uprobe = NULL;
     struct vm_area_struct *vma;
 
     mmap_read_lock(mm);
     vma = vma_lookup(mm, bp_vaddr);
     if (vma) {
         if (valid_vma(vma, false)) {
             struct inode *inode = file_inode(vma->vm_file);
             loff_t offset = vaddr_to_offset(vma, bp_vaddr);
 
             uprobe = find_uprobe(inode, offset);
         }
 
         if (!uprobe)
             *is_swbp = is_trap_at_addr(mm, bp_vaddr);
     } else {
         *is_swbp = -EFAULT;
     }
 
     if (!uprobe && test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags))
         mmf_recalc_uprobes(mm);
     mmap_read_unlock(mm);
 
     return uprobe;
 }
 
 static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 {
     struct uprobe_consumer *uc;
     int remove = UPROBE_HANDLER_REMOVE;
     bool need_prep = false; /* prepare return uprobe, when needed */
 
     down_read(&uprobe->register_rwsem);
     for (uc = uprobe->consumers; uc; uc = uc->next) {
         int rc = 0;
 
         if (uc->handler) {
             rc = uc->handler(uc, regs);
             WARN(rc & ~UPROBE_HANDLER_MASK,
                 "bad rc=0x%x from %ps()\n", rc, uc->handler);
         }
 
         if (uc->ret_handler)
             need_prep = true;
 
         remove &= rc;
     }
 
     if (need_prep && !remove)
         prepare_uretprobe(uprobe, regs); /* put bp at return */
 
     if (remove && uprobe->consumers) {
         WARN_ON(!uprobe_is_active(uprobe));
         unapply_uprobe(uprobe, current->mm);
     }
     up_read(&uprobe->register_rwsem);
 }
 
 static void
 handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
 {
     struct uprobe *uprobe = ri->uprobe;
     struct uprobe_consumer *uc;
 
     down_read(&uprobe->register_rwsem);
     for (uc = uprobe->consumers; uc; uc = uc->next) {
         if (uc->ret_handler)
             uc->ret_handler(uc, ri->func, regs);
     }
     up_read(&uprobe->register_rwsem);
 }
 
 static struct return_instance *find_next_ret_chain(struct return_instance *ri)
 {
     bool chained;
 
     do {
         chained = ri->chained;
         ri = ri->next;  /* can't be NULL if chained */
     } while (chained);
 
     return ri;
 }
 
 static void handle_trampoline(struct pt_regs *regs)
 {
     struct uprobe_task *utask;
     struct return_instance *ri, *next;
     bool valid;
 
     utask = current->utask;
     if (!utask)
         goto sigill;
 
     ri = utask->return_instances;
     if (!ri)
         goto sigill;
 
     do {
         /*
          * We should throw out the frames invalidated by longjmp().
          * If this chain is valid, then the next one should be alive
          * or NULL; the latter case means that nobody but ri->func
          * could hit this trampoline on return. TODO: sigaltstack().
          */
         next = find_next_ret_chain(ri);
         valid = !next || arch_uretprobe_is_alive(next, RP_CHECK_RET, regs);
 
         instruction_pointer_set(regs, ri->orig_ret_vaddr);
         do {
             if (valid)
                 handle_uretprobe_chain(ri, regs);
             ri = free_ret_instance(ri);
             utask->depth--;
         } while (ri != next);
     } while (!valid);
 
     utask->return_instances = ri;
     return;
 
  sigill:
     uprobe_warn(current, "handle uretprobe, sending SIGILL.");
     force_sig(SIGILL);
 
 }
 
 bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs)
 {
     return false;
 }
 
 bool __weak arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
                     struct pt_regs *regs)
 {
     return true;
 }
 
 /*
  * Run handler and ask thread to singlestep.
  * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
  */
 static void handle_swbp(struct pt_regs *regs)
 {
     struct uprobe *uprobe;
     unsigned long bp_vaddr;
     int is_swbp;
 
     bp_vaddr = uprobe_get_swbp_addr(regs);
     if (bp_vaddr == get_trampoline_vaddr())
         return handle_trampoline(regs);
 
     uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
     if (!uprobe) {
         if (is_swbp > 0) {
             /* No matching uprobe; signal SIGTRAP. */
             force_sig(SIGTRAP);
         } else {
             /*
              * Either we raced with uprobe_unregister() or we can't
              * access this memory. The latter is only possible if
              * another thread plays with our ->mm. In both cases
              * we can simply restart. If this vma was unmapped we
              * can pretend this insn was not executed yet and get
              * the (correct) SIGSEGV after restart.
              */
             instruction_pointer_set(regs, bp_vaddr);
         }
         return;
     }
 
     /* change it in advance for ->handler() and restart */
     instruction_pointer_set(regs, bp_vaddr);
 
     /*
      * TODO: move copy_insn/etc into _register and remove this hack.
      * After we hit the bp, _unregister + _register can install the
      * new and not-yet-analyzed uprobe at the same address, restart.
      */
     if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
         goto out;
 
     /*
      * Pairs with the smp_wmb() in prepare_uprobe().
      *
      * Guarantees that if we see the UPROBE_COPY_INSN bit set, then
      * we must also see the stores to &uprobe->arch performed by the
      * prepare_uprobe() call.
      */
     smp_rmb();
 
     /* Tracing handlers use ->utask to communicate with fetch methods */
     if (!get_utask())
         goto out;
 
     if (arch_uprobe_ignore(&uprobe->arch, regs))
         goto out;
 
     handler_chain(uprobe, regs);
 
     if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
         goto out;
 
     if (!pre_ssout(uprobe, regs, bp_vaddr))
         return;
 
     /* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */
 out:
     put_uprobe(uprobe);
 }
 
 /*
  * Perform required fix-ups and disable singlestep.
  * Allow pending signals to take effect.
  */
 static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
 {
     struct uprobe *uprobe;
     int err = 0;
 
     uprobe = utask->active_uprobe;
     if (utask->state == UTASK_SSTEP_ACK)
         err = arch_uprobe_post_xol(&uprobe->arch, regs);
     else if (utask->state == UTASK_SSTEP_TRAPPED)
         arch_uprobe_abort_xol(&uprobe->arch, regs);
     else
         WARN_ON_ONCE(1);
 
     put_uprobe(uprobe);
     utask->active_uprobe = NULL;
     utask->state = UTASK_RUNNING;
     xol_free_insn_slot(current);
 
     spin_lock_irq(&current->sighand->siglock);
     recalc_sigpending(); /* see uprobe_deny_signal() */
     spin_unlock_irq(&current->sighand->siglock);
 
     if (unlikely(err)) {
         uprobe_warn(current, "execute the probed insn, sending SIGILL.");
         force_sig(SIGILL);
     }
 }
 
 /*
  * On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag and
  * allows the thread to return from interrupt. After that handle_swbp()
  * sets utask->active_uprobe.
  *
  * On singlestep exception, singlestep notifier sets the TIF_UPROBE flag
  * and allows the thread to return from interrupt.
  *
  * While returning to userspace, thread notices the TIF_UPROBE flag and calls
  * uprobe_notify_resume().
  */
 void uprobe_notify_resume(struct pt_regs *regs)
 {
     struct uprobe_task *utask;
 
     clear_thread_flag(TIF_UPROBE);
 
     utask = current->utask;
     if (utask && utask->active_uprobe)
         handle_singlestep(utask, regs);
     else
         handle_swbp(regs);
 }
 
 /*
  * uprobe_pre_sstep_notifier gets called from interrupt context as part of
  * notifier mechanism. Set TIF_UPROBE flag and indicate breakpoint hit.
  */
 int uprobe_pre_sstep_notifier(struct pt_regs *regs)
 {
     if (!current->mm)
         return 0;
 
     if (!test_bit(MMF_HAS_UPROBES, &current->mm->flags) &&
         (!current->utask || !current->utask->return_instances))
         return 0;
 
     set_thread_flag(TIF_UPROBE);
     return 1;
 }
 
 /*
  * uprobe_post_sstep_notifier gets called in interrupt context as part of notifier
  * mechanism. Set TIF_UPROBE flag and indicate completion of singlestep.
  */
 int uprobe_post_sstep_notifier(struct pt_regs *regs)
 {
     struct uprobe_task *utask = current->utask;
 
     if (!current->mm || !utask || !utask->active_uprobe)
         /* task is currently not uprobed */
         return 0;
 
     utask->state = UTASK_SSTEP_ACK;
     set_thread_flag(TIF_UPROBE);
     return 1;
 }
 
 static struct notifier_block uprobe_exception_nb = {
     .notifier_call      = arch_uprobe_exception_notify,
     .priority       = INT_MAX-1,    /* notified after kprobes, kgdb */
 };
 
 void __init uprobes_init(void)
 {
     int i;
 
     for (i = 0; i < UPROBES_HASH_SZ; i++)
         mutex_init(&uprobes_mmap_mutex[i]);
 
     BUG_ON(register_die_notifier(&uprobe_exception_nb));
 }

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