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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-only
 /*
  * fs/kernfs/file.c - kernfs file implementation
  *
  * Copyright (c) 2001-3 Patrick Mochel
  * Copyright (c) 2007 SUSE Linux Products GmbH
  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  */
 
 #include <linux/fs.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/poll.h>
 #include <linux/pagemap.h>
 #include <linux/sched/mm.h>
 #include <linux/fsnotify.h>
 #include <linux/uio.h>
 
 #include "kernfs-internal.h"
 
 struct kernfs_open_node {
     struct rcu_head     rcu_head;
     atomic_t        event;
     wait_queue_head_t   poll;
     struct list_head    files; /* goes through kernfs_open_file.list */
 };
 
 /*
  * kernfs_notify() may be called from any context and bounces notifications
  * through a work item.  To minimize space overhead in kernfs_node, the
  * pending queue is implemented as a singly linked list of kernfs_nodes.
  * The list is terminated with the self pointer so that whether a
  * kernfs_node is on the list or not can be determined by testing the next
  * pointer for NULL.
  */
 #define KERNFS_NOTIFY_EOL           ((void *)&kernfs_notify_list)
 
 static DEFINE_SPINLOCK(kernfs_notify_lock);
 static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
 
 static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
 {
     int idx = hash_ptr(kn, NR_KERNFS_LOCK_BITS);
 
     return &kernfs_locks->open_file_mutex[idx];
 }
 
 static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
 {
     struct mutex *lock;
 
     lock = kernfs_open_file_mutex_ptr(kn);
 
     mutex_lock(lock);
 
     return lock;
 }
 
 /**
  * kernfs_deref_open_node - Get kernfs_open_node corresponding to @kn.
  *
  * @of: associated kernfs_open_file instance.
  * @kn: target kernfs_node.
  *
  * Fetch and return ->attr.open of @kn if @of->list is non empty.
  * If @of->list is not empty we can safely assume that @of is on
  * @kn->attr.open->files list and this guarantees that @kn->attr.open
  * will not vanish i.e. dereferencing outside RCU read-side critical
  * section is safe here.
  *
  * The caller needs to make sure that @of->list is not empty.
  */
 static struct kernfs_open_node *
 kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn)
 {
     struct kernfs_open_node *on;
 
     on = rcu_dereference_check(kn->attr.open, !list_empty(&of->list));
 
     return on;
 }
 
 /**
  * kernfs_deref_open_node_protected - Get kernfs_open_node corresponding to @kn
  *
  * @kn: target kernfs_node.
  *
  * Fetch and return ->attr.open of @kn when caller holds the
  * kernfs_open_file_mutex_ptr(kn).
  *
  * Update of ->attr.open happens under kernfs_open_file_mutex_ptr(kn). So when
  * the caller guarantees that this mutex is being held, other updaters can't
  * change ->attr.open and this means that we can safely deref ->attr.open
  * outside RCU read-side critical section.
  *
  * The caller needs to make sure that kernfs_open_file_mutex is held.
  */
 static struct kernfs_open_node *
 kernfs_deref_open_node_protected(struct kernfs_node *kn)
 {
     return rcu_dereference_protected(kn->attr.open,
                 lockdep_is_held(kernfs_open_file_mutex_ptr(kn)));
 }
 
 static struct kernfs_open_file *kernfs_of(struct file *file)
 {
     return ((struct seq_file *)file->private_data)->private;
 }
 
 /*
  * Determine the kernfs_ops for the given kernfs_node.  This function must
  * be called while holding an active reference.
  */
 static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
 {
     if (kn->flags & KERNFS_LOCKDEP)
         lockdep_assert_held(kn);
     return kn->attr.ops;
 }
 
 /*
  * As kernfs_seq_stop() is also called after kernfs_seq_start() or
  * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
  * a seq_file iteration which is fully initialized with an active reference
  * or an aborted kernfs_seq_start() due to get_active failure.  The
  * position pointer is the only context for each seq_file iteration and
  * thus the stop condition should be encoded in it.  As the return value is
  * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
  * choice to indicate get_active failure.
  *
  * Unfortunately, this is complicated due to the optional custom seq_file
  * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
  * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
  * custom seq_file operations and thus can't decide whether put_active
  * should be performed or not only on ERR_PTR(-ENODEV).
  *
  * This is worked around by factoring out the custom seq_stop() and
  * put_active part into kernfs_seq_stop_active(), skipping it from
  * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
  * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
  * that kernfs_seq_stop_active() is skipped only after get_active failure.
  */
 static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
 {
     struct kernfs_open_file *of = sf->private;
     const struct kernfs_ops *ops = kernfs_ops(of->kn);
 
     if (ops->seq_stop)
         ops->seq_stop(sf, v);
     kernfs_put_active(of->kn);
 }
 
 static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
 {
     struct kernfs_open_file *of = sf->private;
     const struct kernfs_ops *ops;
 
     /*
      * @of->mutex nests outside active ref and is primarily to ensure that
      * the ops aren't called concurrently for the same open file.
      */
     mutex_lock(&of->mutex);
     if (!kernfs_get_active(of->kn))
         return ERR_PTR(-ENODEV);
 
     ops = kernfs_ops(of->kn);
     if (ops->seq_start) {
         void *next = ops->seq_start(sf, ppos);
         /* see the comment above kernfs_seq_stop_active() */
         if (next == ERR_PTR(-ENODEV))
             kernfs_seq_stop_active(sf, next);
         return next;
     }
     return single_start(sf, ppos);
 }
 
 static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
 {
     struct kernfs_open_file *of = sf->private;
     const struct kernfs_ops *ops = kernfs_ops(of->kn);
 
     if (ops->seq_next) {
         void *next = ops->seq_next(sf, v, ppos);
         /* see the comment above kernfs_seq_stop_active() */
         if (next == ERR_PTR(-ENODEV))
             kernfs_seq_stop_active(sf, next);
         return next;
     } else {
         /*
          * The same behavior and code as single_open(), always
          * terminate after the initial read.
          */
         ++*ppos;
         return NULL;
     }
 }
 
 static void kernfs_seq_stop(struct seq_file *sf, void *v)
 {
     struct kernfs_open_file *of = sf->private;
 
     if (v != ERR_PTR(-ENODEV))
         kernfs_seq_stop_active(sf, v);
     mutex_unlock(&of->mutex);
 }
 
 static int kernfs_seq_show(struct seq_file *sf, void *v)
 {
     struct kernfs_open_file *of = sf->private;
     struct kernfs_open_node *on = kernfs_deref_open_node(of, of->kn);
 
     if (!on)
         return -EINVAL;
 
     of->event = atomic_read(&on->event);
 
     return of->kn->attr.ops->seq_show(sf, v);
 }
 
 static const struct seq_operations kernfs_seq_ops = {
     .start = kernfs_seq_start,
     .next = kernfs_seq_next,
     .stop = kernfs_seq_stop,
     .show = kernfs_seq_show,
 };
 
 /*
  * As reading a bin file can have side-effects, the exact offset and bytes
  * specified in read(2) call should be passed to the read callback making
  * it difficult to use seq_file.  Implement simplistic custom buffering for
  * bin files.
  */
 static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
     struct kernfs_open_file *of = kernfs_of(iocb->ki_filp);
     ssize_t len = min_t(size_t, iov_iter_count(iter), PAGE_SIZE);
     const struct kernfs_ops *ops;
     struct kernfs_open_node *on;
     char *buf;
 
     buf = of->prealloc_buf;
     if (buf)
         mutex_lock(&of->prealloc_mutex);
     else
         buf = kmalloc(len, GFP_KERNEL);
     if (!buf)
         return -ENOMEM;
 
     /*
      * @of->mutex nests outside active ref and is used both to ensure that
      * the ops aren't called concurrently for the same open file.
      */
     mutex_lock(&of->mutex);
     if (!kernfs_get_active(of->kn)) {
         len = -ENODEV;
         mutex_unlock(&of->mutex);
         goto out_free;
     }
 
     on = kernfs_deref_open_node(of, of->kn);
     if (!on) {
         len = -EINVAL;
         mutex_unlock(&of->mutex);
         goto out_free;
     }
 
     of->event = atomic_read(&on->event);
 
     ops = kernfs_ops(of->kn);
     if (ops->read)
         len = ops->read(of, buf, len, iocb->ki_pos);
     else
         len = -EINVAL;
 
     kernfs_put_active(of->kn);
     mutex_unlock(&of->mutex);
 
     if (len < 0)
         goto out_free;
 
     if (copy_to_iter(buf, len, iter) != len) {
         len = -EFAULT;
         goto out_free;
     }
 
     iocb->ki_pos += len;
 
  out_free:
     if (buf == of->prealloc_buf)
         mutex_unlock(&of->prealloc_mutex);
     else
         kfree(buf);
     return len;
 }
 
 static ssize_t kernfs_fop_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
     if (kernfs_of(iocb->ki_filp)->kn->flags & KERNFS_HAS_SEQ_SHOW)
         return seq_read_iter(iocb, iter);
     return kernfs_file_read_iter(iocb, iter);
 }
 
 /*
  * Copy data in from userland and pass it to the matching kernfs write
  * operation.
  *
  * There is no easy way for us to know if userspace is only doing a partial
  * write, so we don't support them. We expect the entire buffer to come on
  * the first write.  Hint: if you're writing a value, first read the file,
  * modify only the value you're changing, then write entire buffer
  * back.
  */
 static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
     struct kernfs_open_file *of = kernfs_of(iocb->ki_filp);
     ssize_t len = iov_iter_count(iter);
     const struct kernfs_ops *ops;
     char *buf;
 
     if (of->atomic_write_len) {
         if (len > of->atomic_write_len)
             return -E2BIG;
     } else {
         len = min_t(size_t, len, PAGE_SIZE);
     }
 
     buf = of->prealloc_buf;
     if (buf)
         mutex_lock(&of->prealloc_mutex);
     else
         buf = kmalloc(len + 1, GFP_KERNEL);
     if (!buf)
         return -ENOMEM;
 
     if (copy_from_iter(buf, len, iter) != len) {
         len = -EFAULT;
         goto out_free;
     }
     buf[len] = '\0';    /* guarantee string termination */
 
     /*
      * @of->mutex nests outside active ref and is used both to ensure that
      * the ops aren't called concurrently for the same open file.
      */
     mutex_lock(&of->mutex);
     if (!kernfs_get_active(of->kn)) {
         mutex_unlock(&of->mutex);
         len = -ENODEV;
         goto out_free;
     }
 
     ops = kernfs_ops(of->kn);
     if (ops->write)
         len = ops->write(of, buf, len, iocb->ki_pos);
     else
         len = -EINVAL;
 
     kernfs_put_active(of->kn);
     mutex_unlock(&of->mutex);
 
     if (len > 0)
         iocb->ki_pos += len;
 
 out_free:
     if (buf == of->prealloc_buf)
         mutex_unlock(&of->prealloc_mutex);
     else
         kfree(buf);
     return len;
 }
 
 static void kernfs_vma_open(struct vm_area_struct *vma)
 {
     struct file *file = vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
 
     if (!of->vm_ops)
         return;
 
     if (!kernfs_get_active(of->kn))
         return;
 
     if (of->vm_ops->open)
         of->vm_ops->open(vma);
 
     kernfs_put_active(of->kn);
 }
 
 static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf)
 {
     struct file *file = vmf->vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
     vm_fault_t ret;
 
     if (!of->vm_ops)
         return VM_FAULT_SIGBUS;
 
     if (!kernfs_get_active(of->kn))
         return VM_FAULT_SIGBUS;
 
     ret = VM_FAULT_SIGBUS;
     if (of->vm_ops->fault)
         ret = of->vm_ops->fault(vmf);
 
     kernfs_put_active(of->kn);
     return ret;
 }
 
 static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf)
 {
     struct file *file = vmf->vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
     vm_fault_t ret;
 
     if (!of->vm_ops)
         return VM_FAULT_SIGBUS;
 
     if (!kernfs_get_active(of->kn))
         return VM_FAULT_SIGBUS;
 
     ret = 0;
     if (of->vm_ops->page_mkwrite)
         ret = of->vm_ops->page_mkwrite(vmf);
     else
         file_update_time(file);
 
     kernfs_put_active(of->kn);
     return ret;
 }
 
 static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
                  void *buf, int len, int write)
 {
     struct file *file = vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
     int ret;
 
     if (!of->vm_ops)
         return -EINVAL;
 
     if (!kernfs_get_active(of->kn))
         return -EINVAL;
 
     ret = -EINVAL;
     if (of->vm_ops->access)
         ret = of->vm_ops->access(vma, addr, buf, len, write);
 
     kernfs_put_active(of->kn);
     return ret;
 }
 
 #ifdef CONFIG_NUMA
 static int kernfs_vma_set_policy(struct vm_area_struct *vma,
                  struct mempolicy *new)
 {
     struct file *file = vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
     int ret;
 
     if (!of->vm_ops)
         return 0;
 
     if (!kernfs_get_active(of->kn))
         return -EINVAL;
 
     ret = 0;
     if (of->vm_ops->set_policy)
         ret = of->vm_ops->set_policy(vma, new);
 
     kernfs_put_active(of->kn);
     return ret;
 }
 
 static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
                            unsigned long addr)
 {
     struct file *file = vma->vm_file;
     struct kernfs_open_file *of = kernfs_of(file);
     struct mempolicy *pol;
 
     if (!of->vm_ops)
         return vma->vm_policy;
 
     if (!kernfs_get_active(of->kn))
         return vma->vm_policy;
 
     pol = vma->vm_policy;
     if (of->vm_ops->get_policy)
         pol = of->vm_ops->get_policy(vma, addr);
 
     kernfs_put_active(of->kn);
     return pol;
 }
 
 #endif
 
 static const struct vm_operations_struct kernfs_vm_ops = {
     .open       = kernfs_vma_open,
     .fault      = kernfs_vma_fault,
     .page_mkwrite   = kernfs_vma_page_mkwrite,
     .access     = kernfs_vma_access,
 #ifdef CONFIG_NUMA
     .set_policy = kernfs_vma_set_policy,
     .get_policy = kernfs_vma_get_policy,
 #endif
 };
 
 static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 {
     struct kernfs_open_file *of = kernfs_of(file);
     const struct kernfs_ops *ops;
     int rc;
 
     /*
      * mmap path and of->mutex are prone to triggering spurious lockdep
      * warnings and we don't want to add spurious locking dependency
      * between the two.  Check whether mmap is actually implemented
      * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
      * comment in kernfs_file_open() for more details.
      */
     if (!(of->kn->flags & KERNFS_HAS_MMAP))
         return -ENODEV;
 
     mutex_lock(&of->mutex);
 
     rc = -ENODEV;
     if (!kernfs_get_active(of->kn))
         goto out_unlock;
 
     ops = kernfs_ops(of->kn);
     rc = ops->mmap(of, vma);
     if (rc)
         goto out_put;
 
     /*
      * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
      * to satisfy versions of X which crash if the mmap fails: that
      * substitutes a new vm_file, and we don't then want bin_vm_ops.
      */
     if (vma->vm_file != file)
         goto out_put;
 
     rc = -EINVAL;
     if (of->mmapped && of->vm_ops != vma->vm_ops)
         goto out_put;
 
     /*
      * It is not possible to successfully wrap close.
      * So error if someone is trying to use close.
      */
     if (vma->vm_ops && vma->vm_ops->close)
         goto out_put;
 
     rc = 0;
     of->mmapped = true;
     of->vm_ops = vma->vm_ops;
     vma->vm_ops = &kernfs_vm_ops;
 out_put:
     kernfs_put_active(of->kn);
 out_unlock:
     mutex_unlock(&of->mutex);
 
     return rc;
 }
 
 /**
  *  kernfs_get_open_node - get or create kernfs_open_node
  *  @kn: target kernfs_node
  *  @of: kernfs_open_file for this instance of open
  *
  *  If @kn->attr.open exists, increment its reference count; otherwise,
  *  create one.  @of is chained to the files list.
  *
  *  LOCKING:
  *  Kernel thread context (may sleep).
  *
  *  RETURNS:
  *  0 on success, -errno on failure.
  */
 static int kernfs_get_open_node(struct kernfs_node *kn,
                 struct kernfs_open_file *of)
 {
     struct kernfs_open_node *on, *new_on = NULL;
     struct mutex *mutex = NULL;
 
     mutex = kernfs_open_file_mutex_lock(kn);
     on = kernfs_deref_open_node_protected(kn);
 
     if (on) {
         list_add_tail(&of->list, &on->files);
         mutex_unlock(mutex);
         return 0;
     } else {
         /* not there, initialize a new one */
         new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
         if (!new_on) {
             mutex_unlock(mutex);
             return -ENOMEM;
         }
         atomic_set(&new_on->event, 1);
         init_waitqueue_head(&new_on->poll);
         INIT_LIST_HEAD(&new_on->files);
         list_add_tail(&of->list, &new_on->files);
         rcu_assign_pointer(kn->attr.open, new_on);
     }
     mutex_unlock(mutex);
 
     return 0;
 }
 
 /**
  *  kernfs_unlink_open_file - Unlink @of from @kn.
  *
  *  @kn: target kernfs_node
  *  @of: associated kernfs_open_file
  *
  *  Unlink @of from list of @kn's associated open files. If list of
  *  associated open files becomes empty, disassociate and free
  *  kernfs_open_node.
  *
  *  LOCKING:
  *  None.
  */
 static void kernfs_unlink_open_file(struct kernfs_node *kn,
                  struct kernfs_open_file *of)
 {
     struct kernfs_open_node *on;
     struct mutex *mutex = NULL;
 
     mutex = kernfs_open_file_mutex_lock(kn);
 
     on = kernfs_deref_open_node_protected(kn);
     if (!on) {
         mutex_unlock(mutex);
         return;
     }
 
     if (of)
         list_del(&of->list);
 
     if (list_empty(&on->files)) {
         rcu_assign_pointer(kn->attr.open, NULL);
         kfree_rcu(on, rcu_head);
     }
 
     mutex_unlock(mutex);
 }
 
 static int kernfs_fop_open(struct inode *inode, struct file *file)
 {
     struct kernfs_node *kn = inode->i_private;
     struct kernfs_root *root = kernfs_root(kn);
     const struct kernfs_ops *ops;
     struct kernfs_open_file *of;
     bool has_read, has_write, has_mmap;
     int error = -EACCES;
 
     if (!kernfs_get_active(kn))
         return -ENODEV;
 
     ops = kernfs_ops(kn);
 
     has_read = ops->seq_show || ops->read || ops->mmap;
     has_write = ops->write || ops->mmap;
     has_mmap = ops->mmap;
 
     /* see the flag definition for details */
     if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
         if ((file->f_mode & FMODE_WRITE) &&
             (!(inode->i_mode & S_IWUGO) || !has_write))
             goto err_out;
 
         if ((file->f_mode & FMODE_READ) &&
             (!(inode->i_mode & S_IRUGO) || !has_read))
             goto err_out;
     }
 
     /* allocate a kernfs_open_file for the file */
     error = -ENOMEM;
     of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
     if (!of)
         goto err_out;
 
     /*
      * The following is done to give a different lockdep key to
      * @of->mutex for files which implement mmap.  This is a rather
      * crude way to avoid false positive lockdep warning around
      * mm->mmap_lock - mmap nests @of->mutex under mm->mmap_lock and
      * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
      * which mm->mmap_lock nests, while holding @of->mutex.  As each
      * open file has a separate mutex, it's okay as long as those don't
      * happen on the same file.  At this point, we can't easily give
      * each file a separate locking class.  Let's differentiate on
      * whether the file has mmap or not for now.
      *
      * Both paths of the branch look the same.  They're supposed to
      * look that way and give @of->mutex different static lockdep keys.
      */
     if (has_mmap)
         mutex_init(&of->mutex);
     else
         mutex_init(&of->mutex);
 
     of->kn = kn;
     of->file = file;
 
     /*
      * Write path needs to atomic_write_len outside active reference.
      * Cache it in open_file.  See kernfs_fop_write_iter() for details.
      */
     of->atomic_write_len = ops->atomic_write_len;
 
     error = -EINVAL;
     /*
      * ->seq_show is incompatible with ->prealloc,
      * as seq_read does its own allocation.
      * ->read must be used instead.
      */
     if (ops->prealloc && ops->seq_show)
         goto err_free;
     if (ops->prealloc) {
         int len = of->atomic_write_len ?: PAGE_SIZE;
         of->prealloc_buf = kmalloc(len + 1, GFP_KERNEL);
         error = -ENOMEM;
         if (!of->prealloc_buf)
             goto err_free;
         mutex_init(&of->prealloc_mutex);
     }
 
     /*
      * Always instantiate seq_file even if read access doesn't use
      * seq_file or is not requested.  This unifies private data access
      * and readable regular files are the vast majority anyway.
      */
     if (ops->seq_show)
         error = seq_open(file, &kernfs_seq_ops);
     else
         error = seq_open(file, NULL);
     if (error)
         goto err_free;
 
     of->seq_file = file->private_data;
     of->seq_file->private = of;
 
     /* seq_file clears PWRITE unconditionally, restore it if WRITE */
     if (file->f_mode & FMODE_WRITE)
         file->f_mode |= FMODE_PWRITE;
 
     /* make sure we have open node struct */
     error = kernfs_get_open_node(kn, of);
     if (error)
         goto err_seq_release;
 
     if (ops->open) {
         /* nobody has access to @of yet, skip @of->mutex */
         error = ops->open(of);
         if (error)
             goto err_put_node;
     }
 
     /* open succeeded, put active references */
     kernfs_put_active(kn);
     return 0;
 
 err_put_node:
     kernfs_unlink_open_file(kn, of);
 err_seq_release:
     seq_release(inode, file);
 err_free:
     kfree(of->prealloc_buf);
     kfree(of);
 err_out:
     kernfs_put_active(kn);
     return error;
 }
 
 /* used from release/drain to ensure that ->release() is called exactly once */
 static void kernfs_release_file(struct kernfs_node *kn,
                 struct kernfs_open_file *of)
 {
     /*
      * @of is guaranteed to have no other file operations in flight and
      * we just want to synchronize release and drain paths.
      * @kernfs_open_file_mutex_ptr(kn) is enough. @of->mutex can't be used
      * here because drain path may be called from places which can
      * cause circular dependency.
      */
     lockdep_assert_held(kernfs_open_file_mutex_ptr(kn));
 
     if (!of->released) {
         /*
          * A file is never detached without being released and we
          * need to be able to release files which are deactivated
          * and being drained.  Don't use kernfs_ops().
          */
         kn->attr.ops->release(of);
         of->released = true;
     }
 }
 
 static int kernfs_fop_release(struct inode *inode, struct file *filp)
 {
     struct kernfs_node *kn = inode->i_private;
     struct kernfs_open_file *of = kernfs_of(filp);
     struct mutex *mutex = NULL;
 
     if (kn->flags & KERNFS_HAS_RELEASE) {
         mutex = kernfs_open_file_mutex_lock(kn);
         kernfs_release_file(kn, of);
         mutex_unlock(mutex);
     }
 
     kernfs_unlink_open_file(kn, of);
     seq_release(inode, filp);
     kfree(of->prealloc_buf);
     kfree(of);
 
     return 0;
 }
 
 void kernfs_drain_open_files(struct kernfs_node *kn)
 {
     struct kernfs_open_node *on;
     struct kernfs_open_file *of;
     struct mutex *mutex = NULL;
 
     if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
         return;
 
     /*
      * lockless opportunistic check is safe below because no one is adding to
      * ->attr.open at this point of time. This check allows early bail out
      * if ->attr.open is already NULL. kernfs_unlink_open_file makes
      * ->attr.open NULL only while holding kernfs_open_file_mutex so below
      * check under kernfs_open_file_mutex_ptr(kn) will ensure bailing out if
      * ->attr.open became NULL while waiting for the mutex.
      */
     if (!rcu_access_pointer(kn->attr.open))
         return;
 
     mutex = kernfs_open_file_mutex_lock(kn);
     on = kernfs_deref_open_node_protected(kn);
     if (!on) {
         mutex_unlock(mutex);
         return;
     }
 
     list_for_each_entry(of, &on->files, list) {
         struct inode *inode = file_inode(of->file);
 
         if (kn->flags & KERNFS_HAS_MMAP)
             unmap_mapping_range(inode->i_mapping, 0, 0, 1);
 
         if (kn->flags & KERNFS_HAS_RELEASE)
             kernfs_release_file(kn, of);
     }
 
     mutex_unlock(mutex);
 }
 
 /*
  * Kernfs attribute files are pollable.  The idea is that you read
  * the content and then you use 'poll' or 'select' to wait for
  * the content to change.  When the content changes (assuming the
  * manager for the kobject supports notification), poll will
  * return EPOLLERR|EPOLLPRI, and select will return the fd whether
  * it is waiting for read, write, or exceptions.
  * Once poll/select indicates that the value has changed, you
  * need to close and re-open the file, or seek to 0 and read again.
  * Reminder: this only works for attributes which actively support
  * it, and it is not possible to test an attribute from userspace
  * to see if it supports poll (Neither 'poll' nor 'select' return
  * an appropriate error code).  When in doubt, set a suitable timeout value.
  */
 __poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
 {
     struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry);
     struct kernfs_open_node *on = kernfs_deref_open_node(of, kn);
 
     if (!on)
         return EPOLLERR;
 
     poll_wait(of->file, &on->poll, wait);
 
     if (of->event != atomic_read(&on->event))
         return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 
     return DEFAULT_POLLMASK;
 }
 
 static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
 {
     struct kernfs_open_file *of = kernfs_of(filp);
     struct kernfs_node *kn = kernfs_dentry_node(filp->f_path.dentry);
     __poll_t ret;
 
     if (!kernfs_get_active(kn))
         return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 
     if (kn->attr.ops->poll)
         ret = kn->attr.ops->poll(of, wait);
     else
         ret = kernfs_generic_poll(of, wait);
 
     kernfs_put_active(kn);
     return ret;
 }
 
 static void kernfs_notify_workfn(struct work_struct *work)
 {
     struct kernfs_node *kn;
     struct kernfs_super_info *info;
     struct kernfs_root *root;
 repeat:
     /* pop one off the notify_list */
     spin_lock_irq(&kernfs_notify_lock);
     kn = kernfs_notify_list;
     if (kn == KERNFS_NOTIFY_EOL) {
         spin_unlock_irq(&kernfs_notify_lock);
         return;
     }
     kernfs_notify_list = kn->attr.notify_next;
     kn->attr.notify_next = NULL;
     spin_unlock_irq(&kernfs_notify_lock);
 
     root = kernfs_root(kn);
     /* kick fsnotify */
     down_write(&root->kernfs_rwsem);
 
     list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
         struct kernfs_node *parent;
         struct inode *p_inode = NULL;
         struct inode *inode;
         struct qstr name;
 
         /*
          * We want fsnotify_modify() on @kn but as the
          * modifications aren't originating from userland don't
          * have the matching @file available.  Look up the inodes
          * and generate the events manually.
          */
         inode = ilookup(info->sb, kernfs_ino(kn));
         if (!inode)
             continue;
 
         name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
         parent = kernfs_get_parent(kn);
         if (parent) {
             p_inode = ilookup(info->sb, kernfs_ino(parent));
             if (p_inode) {
                 fsnotify(FS_MODIFY | FS_EVENT_ON_CHILD,
                      inode, FSNOTIFY_EVENT_INODE,
                      p_inode, &name, inode, 0);
                 iput(p_inode);
             }
 
             kernfs_put(parent);
         }
 
         if (!p_inode)
             fsnotify_inode(inode, FS_MODIFY);
 
         iput(inode);
     }
 
     up_write(&root->kernfs_rwsem);
     kernfs_put(kn);
     goto repeat;
 }
 
 /**
  * kernfs_notify - notify a kernfs file
  * @kn: file to notify
  *
  * Notify @kn such that poll(2) on @kn wakes up.  Maybe be called from any
  * context.
  */
 void kernfs_notify(struct kernfs_node *kn)
 {
     static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
     unsigned long flags;
     struct kernfs_open_node *on;
 
     if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
         return;
 
     /* kick poll immediately */
     rcu_read_lock();
     on = rcu_dereference(kn->attr.open);
     if (on) {
         atomic_inc(&on->event);
         wake_up_interruptible(&on->poll);
     }
     rcu_read_unlock();
 
     /* schedule work to kick fsnotify */
     spin_lock_irqsave(&kernfs_notify_lock, flags);
     if (!kn->attr.notify_next) {
         kernfs_get(kn);
         kn->attr.notify_next = kernfs_notify_list;
         kernfs_notify_list = kn;
         schedule_work(&kernfs_notify_work);
     }
     spin_unlock_irqrestore(&kernfs_notify_lock, flags);
 }
 EXPORT_SYMBOL_GPL(kernfs_notify);
 
 const struct file_operations kernfs_file_fops = {
     .read_iter  = kernfs_fop_read_iter,
     .write_iter = kernfs_fop_write_iter,
     .llseek     = generic_file_llseek,
     .mmap       = kernfs_fop_mmap,
     .open       = kernfs_fop_open,
     .release    = kernfs_fop_release,
     .poll       = kernfs_fop_poll,
     .fsync      = noop_fsync,
     .splice_read    = generic_file_splice_read,
     .splice_write   = iter_file_splice_write,
 };
 
 /**
  * __kernfs_create_file - kernfs internal function to create a file
  * @parent: directory to create the file in
  * @name: name of the file
  * @mode: mode of the file
  * @uid: uid of the file
  * @gid: gid of the file
  * @size: size of the file
  * @ops: kernfs operations for the file
  * @priv: private data for the file
  * @ns: optional namespace tag of the file
  * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
  *
  * Returns the created node on success, ERR_PTR() value on error.
  */
 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
                      const char *name,
                      umode_t mode, kuid_t uid, kgid_t gid,
                      loff_t size,
                      const struct kernfs_ops *ops,
                      void *priv, const void *ns,
                      struct lock_class_key *key)
 {
     struct kernfs_node *kn;
     unsigned flags;
     int rc;
 
     flags = KERNFS_FILE;
 
     kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG,
                  uid, gid, flags);
     if (!kn)
         return ERR_PTR(-ENOMEM);
 
     kn->attr.ops = ops;
     kn->attr.size = size;
     kn->ns = ns;
     kn->priv = priv;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     if (key) {
         lockdep_init_map(&kn->dep_map, "kn->active", key, 0);
         kn->flags |= KERNFS_LOCKDEP;
     }
 #endif
 
     /*
      * kn->attr.ops is accessible only while holding active ref.  We
      * need to know whether some ops are implemented outside active
      * ref.  Cache their existence in flags.
      */
     if (ops->seq_show)
         kn->flags |= KERNFS_HAS_SEQ_SHOW;
     if (ops->mmap)
         kn->flags |= KERNFS_HAS_MMAP;
     if (ops->release)
         kn->flags |= KERNFS_HAS_RELEASE;
 
     rc = kernfs_add_one(kn);
     if (rc) {
         kernfs_put(kn);
         return ERR_PTR(rc);
     }
     return kn;
 }

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