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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-or-later
 
 #include <linux/slab.h>
 #include <linux/sched/task.h>
 
 #include "futex.h"
 #include "../locking/rtmutex_common.h"
 
 /*
  * PI code:
  */
 int refill_pi_state_cache(void)
 {
     struct futex_pi_state *pi_state;
 
     if (likely(current->pi_state_cache))
         return 0;
 
     pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
 
     if (!pi_state)
         return -ENOMEM;
 
     INIT_LIST_HEAD(&pi_state->list);
     /* pi_mutex gets initialized later */
     pi_state->owner = NULL;
     refcount_set(&pi_state->refcount, 1);
     pi_state->key = FUTEX_KEY_INIT;
 
     current->pi_state_cache = pi_state;
 
     return 0;
 }
 
 static struct futex_pi_state *alloc_pi_state(void)
 {
     struct futex_pi_state *pi_state = current->pi_state_cache;
 
     WARN_ON(!pi_state);
     current->pi_state_cache = NULL;
 
     return pi_state;
 }
 
 static void pi_state_update_owner(struct futex_pi_state *pi_state,
                   struct task_struct *new_owner)
 {
     struct task_struct *old_owner = pi_state->owner;
 
     lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
 
     if (old_owner) {
         raw_spin_lock(&old_owner->pi_lock);
         WARN_ON(list_empty(&pi_state->list));
         list_del_init(&pi_state->list);
         raw_spin_unlock(&old_owner->pi_lock);
     }
 
     if (new_owner) {
         raw_spin_lock(&new_owner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &new_owner->pi_state_list);
         pi_state->owner = new_owner;
         raw_spin_unlock(&new_owner->pi_lock);
     }
 }
 
 void get_pi_state(struct futex_pi_state *pi_state)
 {
     WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
 }
 
 /*
  * Drops a reference to the pi_state object and frees or caches it
  * when the last reference is gone.
  */
 void put_pi_state(struct futex_pi_state *pi_state)
 {
     if (!pi_state)
         return;
 
     if (!refcount_dec_and_test(&pi_state->refcount))
         return;
 
     /*
      * If pi_state->owner is NULL, the owner is most probably dying
      * and has cleaned up the pi_state already
      */
     if (pi_state->owner) {
         unsigned long flags;
 
         raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
         pi_state_update_owner(pi_state, NULL);
         rt_mutex_proxy_unlock(&pi_state->pi_mutex);
         raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
     }
 
     if (current->pi_state_cache) {
         kfree(pi_state);
     } else {
         /*
          * pi_state->list is already empty.
          * clear pi_state->owner.
          * refcount is at 0 - put it back to 1.
          */
         pi_state->owner = NULL;
         refcount_set(&pi_state->refcount, 1);
         current->pi_state_cache = pi_state;
     }
 }
 
 /*
  * We need to check the following states:
  *
  *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
  *
  * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
  * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
  *
  * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
  *
  * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
  * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
  *
  * [6]  Found  | Found    | task      | 0         | 1      | Valid
  *
  * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
  *
  * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
  * [9]  Found  | Found    | task      | 0         | 0      | Invalid
  * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
  *
  * [1]  Indicates that the kernel can acquire the futex atomically. We
  *  came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
  *
  * [2]  Valid, if TID does not belong to a kernel thread. If no matching
  *      thread is found then it indicates that the owner TID has died.
  *
  * [3]  Invalid. The waiter is queued on a non PI futex
  *
  * [4]  Valid state after exit_robust_list(), which sets the user space
  *  value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
  *
  * [5]  The user space value got manipulated between exit_robust_list()
  *  and exit_pi_state_list()
  *
  * [6]  Valid state after exit_pi_state_list() which sets the new owner in
  *  the pi_state but cannot access the user space value.
  *
  * [7]  pi_state->owner can only be NULL when the OWNER_DIED bit is set.
  *
  * [8]  Owner and user space value match
  *
  * [9]  There is no transient state which sets the user space TID to 0
  *  except exit_robust_list(), but this is indicated by the
  *  FUTEX_OWNER_DIED bit. See [4]
  *
  * [10] There is no transient state which leaves owner and user space
  *  TID out of sync. Except one error case where the kernel is denied
  *  write access to the user address, see fixup_pi_state_owner().
  *
  *
  * Serialization and lifetime rules:
  *
  * hb->lock:
  *
  *  hb -> futex_q, relation
  *  futex_q -> pi_state, relation
  *
  *  (cannot be raw because hb can contain arbitrary amount
  *   of futex_q's)
  *
  * pi_mutex->wait_lock:
  *
  *  {uval, pi_state}
  *
  *  (and pi_mutex 'obviously')
  *
  * p->pi_lock:
  *
  *  p->pi_state_list -> pi_state->list, relation
  *  pi_mutex->owner -> pi_state->owner, relation
  *
  * pi_state->refcount:
  *
  *  pi_state lifetime
  *
  *
  * Lock order:
  *
  *   hb->lock
  *     pi_mutex->wait_lock
  *       p->pi_lock
  *
  */
 
 /*
  * Validate that the existing waiter has a pi_state and sanity check
  * the pi_state against the user space value. If correct, attach to
  * it.
  */
 static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
                   struct futex_pi_state *pi_state,
                   struct futex_pi_state **ps)
 {
     pid_t pid = uval & FUTEX_TID_MASK;
     u32 uval2;
     int ret;
 
     /*
      * Userspace might have messed up non-PI and PI futexes [3]
      */
     if (unlikely(!pi_state))
         return -EINVAL;
 
     /*
      * We get here with hb->lock held, and having found a
      * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
      * has dropped the hb->lock in between futex_queue() and futex_unqueue_pi(),
      * which in turn means that futex_lock_pi() still has a reference on
      * our pi_state.
      *
      * The waiter holding a reference on @pi_state also protects against
      * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
      * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
      * free pi_state before we can take a reference ourselves.
      */
     WARN_ON(!refcount_read(&pi_state->refcount));
 
     /*
      * Now that we have a pi_state, we can acquire wait_lock
      * and do the state validation.
      */
     raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
     /*
      * Since {uval, pi_state} is serialized by wait_lock, and our current
      * uval was read without holding it, it can have changed. Verify it
      * still is what we expect it to be, otherwise retry the entire
      * operation.
      */
     if (futex_get_value_locked(&uval2, uaddr))
         goto out_efault;
 
     if (uval != uval2)
         goto out_eagain;
 
     /*
      * Handle the owner died case:
      */
     if (uval & FUTEX_OWNER_DIED) {
         /*
          * exit_pi_state_list sets owner to NULL and wakes the
          * topmost waiter. The task which acquires the
          * pi_state->rt_mutex will fixup owner.
          */
         if (!pi_state->owner) {
             /*
              * No pi state owner, but the user space TID
              * is not 0. Inconsistent state. [5]
              */
             if (pid)
                 goto out_einval;
             /*
              * Take a ref on the state and return success. [4]
              */
             goto out_attach;
         }
 
         /*
          * If TID is 0, then either the dying owner has not
          * yet executed exit_pi_state_list() or some waiter
          * acquired the rtmutex in the pi state, but did not
          * yet fixup the TID in user space.
          *
          * Take a ref on the state and return success. [6]
          */
         if (!pid)
             goto out_attach;
     } else {
         /*
          * If the owner died bit is not set, then the pi_state
          * must have an owner. [7]
          */
         if (!pi_state->owner)
             goto out_einval;
     }
 
     /*
      * Bail out if user space manipulated the futex value. If pi
      * state exists then the owner TID must be the same as the
      * user space TID. [9/10]
      */
     if (pid != task_pid_vnr(pi_state->owner))
         goto out_einval;
 
 out_attach:
     get_pi_state(pi_state);
     raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
     *ps = pi_state;
     return 0;
 
 out_einval:
     ret = -EINVAL;
     goto out_error;
 
 out_eagain:
     ret = -EAGAIN;
     goto out_error;
 
 out_efault:
     ret = -EFAULT;
     goto out_error;
 
 out_error:
     raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
     return ret;
 }
 
 static int handle_exit_race(u32 __user *uaddr, u32 uval,
                 struct task_struct *tsk)
 {
     u32 uval2;
 
     /*
      * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
      * caller that the alleged owner is busy.
      */
     if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
         return -EBUSY;
 
     /*
      * Reread the user space value to handle the following situation:
      *
      * CPU0             CPU1
      *
      * sys_exit()           sys_futex()
      *  do_exit()            futex_lock_pi()
      *                                futex_lock_pi_atomic()
      *   exit_signals(tsk)          No waiters:
      *    tsk->flags |= PF_EXITING;     *uaddr == 0x00000PID
      *  mm_release(tsk)         Set waiter bit
      *   exit_robust_list(tsk) {        *uaddr = 0x80000PID;
      *      Set owner died          attach_to_pi_owner() {
      *    *uaddr = 0xC0000000;       tsk = get_task(PID);
      *   }                   if (!tsk->flags & PF_EXITING) {
      *  ...                    attach();
      *  tsk->futex_state =               } else {
      *  FUTEX_STATE_DEAD;              if (tsk->futex_state !=
      *                    FUTEX_STATE_DEAD)
      *                       return -EAGAIN;
      *                     return -ESRCH; <--- FAIL
      *                   }
      *
      * Returning ESRCH unconditionally is wrong here because the
      * user space value has been changed by the exiting task.
      *
      * The same logic applies to the case where the exiting task is
      * already gone.
      */
     if (futex_get_value_locked(&uval2, uaddr))
         return -EFAULT;
 
     /* If the user space value has changed, try again. */
     if (uval2 != uval)
         return -EAGAIN;
 
     /*
      * The exiting task did not have a robust list, the robust list was
      * corrupted or the user space value in *uaddr is simply bogus.
      * Give up and tell user space.
      */
     return -ESRCH;
 }
 
 static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
                  struct futex_pi_state **ps)
 {
     /*
      * No existing pi state. First waiter. [2]
      *
      * This creates pi_state, we have hb->lock held, this means nothing can
      * observe this state, wait_lock is irrelevant.
      */
     struct futex_pi_state *pi_state = alloc_pi_state();
 
     /*
      * Initialize the pi_mutex in locked state and make @p
      * the owner of it:
      */
     rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 
     /* Store the key for possible exit cleanups: */
     pi_state->key = *key;
 
     WARN_ON(!list_empty(&pi_state->list));
     list_add(&pi_state->list, &p->pi_state_list);
     /*
      * Assignment without holding pi_state->pi_mutex.wait_lock is safe
      * because there is no concurrency as the object is not published yet.
      */
     pi_state->owner = p;
 
     *ps = pi_state;
 }
 /*
  * Lookup the task for the TID provided from user space and attach to
  * it after doing proper sanity checks.
  */
 static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
                   struct futex_pi_state **ps,
                   struct task_struct **exiting)
 {
     pid_t pid = uval & FUTEX_TID_MASK;
     struct task_struct *p;
 
     /*
      * We are the first waiter - try to look up the real owner and attach
      * the new pi_state to it, but bail out when TID = 0 [1]
      *
      * The !pid check is paranoid. None of the call sites should end up
      * with pid == 0, but better safe than sorry. Let the caller retry
      */
     if (!pid)
         return -EAGAIN;
     p = find_get_task_by_vpid(pid);
     if (!p)
         return handle_exit_race(uaddr, uval, NULL);
 
     if (unlikely(p->flags & PF_KTHREAD)) {
         put_task_struct(p);
         return -EPERM;
     }
 
     /*
      * We need to look at the task state to figure out, whether the
      * task is exiting. To protect against the change of the task state
      * in futex_exit_release(), we do this protected by p->pi_lock:
      */
     raw_spin_lock_irq(&p->pi_lock);
     if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
         /*
          * The task is on the way out. When the futex state is
          * FUTEX_STATE_DEAD, we know that the task has finished
          * the cleanup:
          */
         int ret = handle_exit_race(uaddr, uval, p);
 
         raw_spin_unlock_irq(&p->pi_lock);
         /*
          * If the owner task is between FUTEX_STATE_EXITING and
          * FUTEX_STATE_DEAD then store the task pointer and keep
          * the reference on the task struct. The calling code will
          * drop all locks, wait for the task to reach
          * FUTEX_STATE_DEAD and then drop the refcount. This is
          * required to prevent a live lock when the current task
          * preempted the exiting task between the two states.
          */
         if (ret == -EBUSY)
             *exiting = p;
         else
             put_task_struct(p);
         return ret;
     }
 
     __attach_to_pi_owner(p, key, ps);
     raw_spin_unlock_irq(&p->pi_lock);
 
     put_task_struct(p);
 
     return 0;
 }
 
 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
 {
     int err;
     u32 curval;
 
     if (unlikely(should_fail_futex(true)))
         return -EFAULT;
 
     err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
     if (unlikely(err))
         return err;
 
     /* If user space value changed, let the caller retry */
     return curval != uval ? -EAGAIN : 0;
 }
 
 /**
  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
  * @uaddr:      the pi futex user address
  * @hb:         the pi futex hash bucket
  * @key:        the futex key associated with uaddr and hb
  * @ps:         the pi_state pointer where we store the result of the
  *          lookup
  * @task:       the task to perform the atomic lock work for.  This will
  *          be "current" except in the case of requeue pi.
  * @exiting:        Pointer to store the task pointer of the owner task
  *          which is in the middle of exiting
  * @set_waiters:    force setting the FUTEX_WAITERS bit (1) or not (0)
  *
  * Return:
  *  -  0 - ready to wait;
  *  -  1 - acquired the lock;
  *  - <0 - error
  *
  * The hb->lock must be held by the caller.
  *
  * @exiting is only set when the return value is -EBUSY. If so, this holds
  * a refcount on the exiting task on return and the caller needs to drop it
  * after waiting for the exit to complete.
  */
 int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
              union futex_key *key,
              struct futex_pi_state **ps,
              struct task_struct *task,
              struct task_struct **exiting,
              int set_waiters)
 {
     u32 uval, newval, vpid = task_pid_vnr(task);
     struct futex_q *top_waiter;
     int ret;
 
     /*
      * Read the user space value first so we can validate a few
      * things before proceeding further.
      */
     if (futex_get_value_locked(&uval, uaddr))
         return -EFAULT;
 
     if (unlikely(should_fail_futex(true)))
         return -EFAULT;
 
     /*
      * Detect deadlocks.
      */
     if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
         return -EDEADLK;
 
     if ((unlikely(should_fail_futex(true))))
         return -EDEADLK;
 
     /*
      * Lookup existing state first. If it exists, try to attach to
      * its pi_state.
      */
     top_waiter = futex_top_waiter(hb, key);
     if (top_waiter)
         return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
 
     /*
      * No waiter and user TID is 0. We are here because the
      * waiters or the owner died bit is set or called from
      * requeue_cmp_pi or for whatever reason something took the
      * syscall.
      */
     if (!(uval & FUTEX_TID_MASK)) {
         /*
          * We take over the futex. No other waiters and the user space
          * TID is 0. We preserve the owner died bit.
          */
         newval = uval & FUTEX_OWNER_DIED;
         newval |= vpid;
 
         /* The futex requeue_pi code can enforce the waiters bit */
         if (set_waiters)
             newval |= FUTEX_WAITERS;
 
         ret = lock_pi_update_atomic(uaddr, uval, newval);
         if (ret)
             return ret;
 
         /*
          * If the waiter bit was requested the caller also needs PI
          * state attached to the new owner of the user space futex.
          *
          * @task is guaranteed to be alive and it cannot be exiting
          * because it is either sleeping or waiting in
          * futex_requeue_pi_wakeup_sync().
          *
          * No need to do the full attach_to_pi_owner() exercise
          * because @task is known and valid.
          */
         if (set_waiters) {
             raw_spin_lock_irq(&task->pi_lock);
             __attach_to_pi_owner(task, key, ps);
             raw_spin_unlock_irq(&task->pi_lock);
         }
         return 1;
     }
 
     /*
      * First waiter. Set the waiters bit before attaching ourself to
      * the owner. If owner tries to unlock, it will be forced into
      * the kernel and blocked on hb->lock.
      */
     newval = uval | FUTEX_WAITERS;
     ret = lock_pi_update_atomic(uaddr, uval, newval);
     if (ret)
         return ret;
     /*
      * If the update of the user space value succeeded, we try to
      * attach to the owner. If that fails, no harm done, we only
      * set the FUTEX_WAITERS bit in the user space variable.
      */
     return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
 }
 
 /*
  * Caller must hold a reference on @pi_state.
  */
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
 {
     struct rt_mutex_waiter *top_waiter;
     struct task_struct *new_owner;
     bool postunlock = false;
     DEFINE_RT_WAKE_Q(wqh);
     u32 curval, newval;
     int ret = 0;
 
     top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
     if (WARN_ON_ONCE(!top_waiter)) {
         /*
          * As per the comment in futex_unlock_pi() this should not happen.
          *
          * When this happens, give up our locks and try again, giving
          * the futex_lock_pi() instance time to complete, either by
          * waiting on the rtmutex or removing itself from the futex
          * queue.
          */
         ret = -EAGAIN;
         goto out_unlock;
     }
 
     new_owner = top_waiter->task;
 
     /*
      * We pass it to the next owner. The WAITERS bit is always kept
      * enabled while there is PI state around. We cleanup the owner
      * died bit, because we are the owner.
      */
     newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
 
     if (unlikely(should_fail_futex(true))) {
         ret = -EFAULT;
         goto out_unlock;
     }
 
     ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
     if (!ret && (curval != uval)) {
         /*
          * If a unconditional UNLOCK_PI operation (user space did not
          * try the TID->0 transition) raced with a waiter setting the
          * FUTEX_WAITERS flag between get_user() and locking the hash
          * bucket lock, retry the operation.
          */
         if ((FUTEX_TID_MASK & curval) == uval)
             ret = -EAGAIN;
         else
             ret = -EINVAL;
     }
 
     if (!ret) {
         /*
          * This is a point of no return; once we modified the uval
          * there is no going back and subsequent operations must
          * not fail.
          */
         pi_state_update_owner(pi_state, new_owner);
         postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
     }
 
 out_unlock:
     raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
 
     if (postunlock)
         rt_mutex_postunlock(&wqh);
 
     return ret;
 }
 
 static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
                   struct task_struct *argowner)
 {
     struct futex_pi_state *pi_state = q->pi_state;
     struct task_struct *oldowner, *newowner;
     u32 uval, curval, newval, newtid;
     int err = 0;
 
     oldowner = pi_state->owner;
 
     /*
      * We are here because either:
      *
      *  - we stole the lock and pi_state->owner needs updating to reflect
      *    that (@argowner == current),
      *
      * or:
      *
      *  - someone stole our lock and we need to fix things to point to the
      *    new owner (@argowner == NULL).
      *
      * Either way, we have to replace the TID in the user space variable.
      * This must be atomic as we have to preserve the owner died bit here.
      *
      * Note: We write the user space value _before_ changing the pi_state
      * because we can fault here. Imagine swapped out pages or a fork
      * that marked all the anonymous memory readonly for cow.
      *
      * Modifying pi_state _before_ the user space value would leave the
      * pi_state in an inconsistent state when we fault here, because we
      * need to drop the locks to handle the fault. This might be observed
      * in the PID checks when attaching to PI state .
      */
 retry:
     if (!argowner) {
         if (oldowner != current) {
             /*
              * We raced against a concurrent self; things are
              * already fixed up. Nothing to do.
              */
             return 0;
         }
 
         if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
             /* We got the lock. pi_state is correct. Tell caller. */
             return 1;
         }
 
         /*
          * The trylock just failed, so either there is an owner or
          * there is a higher priority waiter than this one.
          */
         newowner = rt_mutex_owner(&pi_state->pi_mutex);
         /*
          * If the higher priority waiter has not yet taken over the
          * rtmutex then newowner is NULL. We can't return here with
          * that state because it's inconsistent vs. the user space
          * state. So drop the locks and try again. It's a valid
          * situation and not any different from the other retry
          * conditions.
          */
         if (unlikely(!newowner)) {
             err = -EAGAIN;
             goto handle_err;
         }
     } else {
         WARN_ON_ONCE(argowner != current);
         if (oldowner == current) {
             /*
              * We raced against a concurrent self; things are
              * already fixed up. Nothing to do.
              */
             return 1;
         }
         newowner = argowner;
     }
 
     newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
     /* Owner died? */
     if (!pi_state->owner)
         newtid |= FUTEX_OWNER_DIED;
 
     err = futex_get_value_locked(&uval, uaddr);
     if (err)
         goto handle_err;
 
     for (;;) {
         newval = (uval & FUTEX_OWNER_DIED) | newtid;
 
         err = futex_cmpxchg_value_locked(&curval, uaddr, uval, newval);
         if (err)
             goto handle_err;
 
         if (curval == uval)
             break;
         uval = curval;
     }
 
     /*
      * We fixed up user space. Now we need to fix the pi_state
      * itself.
      */
     pi_state_update_owner(pi_state, newowner);
 
     return argowner == current;
 
     /*
      * In order to reschedule or handle a page fault, we need to drop the
      * locks here. In the case of a fault, this gives the other task
      * (either the highest priority waiter itself or the task which stole
      * the rtmutex) the chance to try the fixup of the pi_state. So once we
      * are back from handling the fault we need to check the pi_state after
      * reacquiring the locks and before trying to do another fixup. When
      * the fixup has been done already we simply return.
      *
      * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
      * drop hb->lock since the caller owns the hb -> futex_q relation.
      * Dropping the pi_mutex->wait_lock requires the state revalidate.
      */
 handle_err:
     raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
     spin_unlock(q->lock_ptr);
 
     switch (err) {
     case -EFAULT:
         err = fault_in_user_writeable(uaddr);
         break;
 
     case -EAGAIN:
         cond_resched();
         err = 0;
         break;
 
     default:
         WARN_ON_ONCE(1);
         break;
     }
 
     spin_lock(q->lock_ptr);
     raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
     /*
      * Check if someone else fixed it for us:
      */
     if (pi_state->owner != oldowner)
         return argowner == current;
 
     /* Retry if err was -EAGAIN or the fault in succeeded */
     if (!err)
         goto retry;
 
     /*
      * fault_in_user_writeable() failed so user state is immutable. At
      * best we can make the kernel state consistent but user state will
      * be most likely hosed and any subsequent unlock operation will be
      * rejected due to PI futex rule [10].
      *
      * Ensure that the rtmutex owner is also the pi_state owner despite
      * the user space value claiming something different. There is no
      * point in unlocking the rtmutex if current is the owner as it
      * would need to wait until the next waiter has taken the rtmutex
      * to guarantee consistent state. Keep it simple. Userspace asked
      * for this wreckaged state.
      *
      * The rtmutex has an owner - either current or some other
      * task. See the EAGAIN loop above.
      */
     pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
 
     return err;
 }
 
 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
                 struct task_struct *argowner)
 {
     struct futex_pi_state *pi_state = q->pi_state;
     int ret;
 
     lockdep_assert_held(q->lock_ptr);
 
     raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
     ret = __fixup_pi_state_owner(uaddr, q, argowner);
     raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
     return ret;
 }
 
 /**
  * fixup_pi_owner() - Post lock pi_state and corner case management
  * @uaddr:  user address of the futex
  * @q:      futex_q (contains pi_state and access to the rt_mutex)
  * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
  *
  * After attempting to lock an rt_mutex, this function is called to cleanup
  * the pi_state owner as well as handle race conditions that may allow us to
  * acquire the lock. Must be called with the hb lock held.
  *
  * Return:
  *  -  1 - success, lock taken;
  *  -  0 - success, lock not taken;
  *  - <0 - on error (-EFAULT)
  */
 int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked)
 {
     if (locked) {
         /*
          * Got the lock. We might not be the anticipated owner if we
          * did a lock-steal - fix up the PI-state in that case:
          *
          * Speculative pi_state->owner read (we don't hold wait_lock);
          * since we own the lock pi_state->owner == current is the
          * stable state, anything else needs more attention.
          */
         if (q->pi_state->owner != current)
             return fixup_pi_state_owner(uaddr, q, current);
         return 1;
     }
 
     /*
      * If we didn't get the lock; check if anybody stole it from us. In
      * that case, we need to fix up the uval to point to them instead of
      * us, otherwise bad things happen. [10]
      *
      * Another speculative read; pi_state->owner == current is unstable
      * but needs our attention.
      */
     if (q->pi_state->owner == current)
         return fixup_pi_state_owner(uaddr, q, NULL);
 
     /*
      * Paranoia check. If we did not take the lock, then we should not be
      * the owner of the rt_mutex. Warn and establish consistent state.
      */
     if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
         return fixup_pi_state_owner(uaddr, q, current);
 
     return 0;
 }
 
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation:
  * if there are waiters then it will block as a consequence of relying
  * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
  * a 0 value of the futex too.).
  *
  * Also serves as futex trylock_pi()'ing, and due semantics.
  */
 int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock)
 {
     struct hrtimer_sleeper timeout, *to;
     struct task_struct *exiting = NULL;
     struct rt_mutex_waiter rt_waiter;
     struct futex_hash_bucket *hb;
     struct futex_q q = futex_q_init;
     int res, ret;
 
     if (!IS_ENABLED(CONFIG_FUTEX_PI))
         return -ENOSYS;
 
     if (refill_pi_state_cache())
         return -ENOMEM;
 
     to = futex_setup_timer(time, &timeout, flags, 0);
 
 retry:
     ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
     if (unlikely(ret != 0))
         goto out;
 
 retry_private:
     hb = futex_q_lock(&q);
 
     ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
                    &exiting, 0);
     if (unlikely(ret)) {
         /*
          * Atomic work succeeded and we got the lock,
          * or failed. Either way, we do _not_ block.
          */
         switch (ret) {
         case 1:
             /* We got the lock. */
             ret = 0;
             goto out_unlock_put_key;
         case -EFAULT:
             goto uaddr_faulted;
         case -EBUSY:
         case -EAGAIN:
             /*
              * Two reasons for this:
              * - EBUSY: Task is exiting and we just wait for the
              *   exit to complete.
              * - EAGAIN: The user space value changed.
              */
             futex_q_unlock(hb);
             /*
              * Handle the case where the owner is in the middle of
              * exiting. Wait for the exit to complete otherwise
              * this task might loop forever, aka. live lock.
              */
             wait_for_owner_exiting(ret, exiting);
             cond_resched();
             goto retry;
         default:
             goto out_unlock_put_key;
         }
     }
 
     WARN_ON(!q.pi_state);
 
     /*
      * Only actually queue now that the atomic ops are done:
      */
     __futex_queue(&q, hb);
 
     if (trylock) {
         ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
         /* Fixup the trylock return value: */
         ret = ret ? 0 : -EWOULDBLOCK;
         goto no_block;
     }
 
     rt_mutex_init_waiter(&rt_waiter);
 
     /*
      * On PREEMPT_RT, when hb->lock becomes an rt_mutex, we must not
      * hold it while doing rt_mutex_start_proxy(), because then it will
      * include hb->lock in the blocking chain, even through we'll not in
      * fact hold it while blocking. This will lead it to report -EDEADLK
      * and BUG when futex_unlock_pi() interleaves with this.
      *
      * Therefore acquire wait_lock while holding hb->lock, but drop the
      * latter before calling __rt_mutex_start_proxy_lock(). This
      * interleaves with futex_unlock_pi() -- which does a similar lock
      * handoff -- such that the latter can observe the futex_q::pi_state
      * before __rt_mutex_start_proxy_lock() is done.
      */
     raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
     spin_unlock(q.lock_ptr);
     /*
      * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
      * such that futex_unlock_pi() is guaranteed to observe the waiter when
      * it sees the futex_q::pi_state.
      */
     ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
     raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
 
     if (ret) {
         if (ret == 1)
             ret = 0;
         goto cleanup;
     }
 
     if (unlikely(to))
         hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
 
     ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
 
 cleanup:
     spin_lock(q.lock_ptr);
     /*
      * If we failed to acquire the lock (deadlock/signal/timeout), we must
      * first acquire the hb->lock before removing the lock from the
      * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
      * lists consistent.
      *
      * In particular; it is important that futex_unlock_pi() can not
      * observe this inconsistency.
      */
     if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
         ret = 0;
 
 no_block:
     /*
      * Fixup the pi_state owner and possibly acquire the lock if we
      * haven't already.
      */
     res = fixup_pi_owner(uaddr, &q, !ret);
     /*
      * If fixup_pi_owner() returned an error, propagate that.  If it acquired
      * the lock, clear our -ETIMEDOUT or -EINTR.
      */
     if (res)
         ret = (res < 0) ? res : 0;
 
     futex_unqueue_pi(&q);
     spin_unlock(q.lock_ptr);
     goto out;
 
 out_unlock_put_key:
     futex_q_unlock(hb);
 
 out:
     if (to) {
         hrtimer_cancel(&to->timer);
         destroy_hrtimer_on_stack(&to->timer);
     }
     return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
     futex_q_unlock(hb);
 
     ret = fault_in_user_writeable(uaddr);
     if (ret)
         goto out;
 
     if (!(flags & FLAGS_SHARED))
         goto retry_private;
 
     goto retry;
 }
 
 /*
  * Userspace attempted a TID -> 0 atomic transition, and failed.
  * This is the in-kernel slowpath: we look up the PI state (if any),
  * and do the rt-mutex unlock.
  */
 int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 {
     u32 curval, uval, vpid = task_pid_vnr(current);
     union futex_key key = FUTEX_KEY_INIT;
     struct futex_hash_bucket *hb;
     struct futex_q *top_waiter;
     int ret;
 
     if (!IS_ENABLED(CONFIG_FUTEX_PI))
         return -ENOSYS;
 
 retry:
     if (get_user(uval, uaddr))
         return -EFAULT;
     /*
      * We release only a lock we actually own:
      */
     if ((uval & FUTEX_TID_MASK) != vpid)
         return -EPERM;
 
     ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
     if (ret)
         return ret;
 
     hb = futex_hash(&key);
     spin_lock(&hb->lock);
 
     /*
      * Check waiters first. We do not trust user space values at
      * all and we at least want to know if user space fiddled
      * with the futex value instead of blindly unlocking.
      */
     top_waiter = futex_top_waiter(hb, &key);
     if (top_waiter) {
         struct futex_pi_state *pi_state = top_waiter->pi_state;
 
         ret = -EINVAL;
         if (!pi_state)
             goto out_unlock;
 
         /*
          * If current does not own the pi_state then the futex is
          * inconsistent and user space fiddled with the futex value.
          */
         if (pi_state->owner != current)
             goto out_unlock;
 
         get_pi_state(pi_state);
         /*
          * By taking wait_lock while still holding hb->lock, we ensure
          * there is no point where we hold neither; and therefore
          * wake_futex_p() must observe a state consistent with what we
          * observed.
          *
          * In particular; this forces __rt_mutex_start_proxy() to
          * complete such that we're guaranteed to observe the
          * rt_waiter. Also see the WARN in wake_futex_pi().
          */
         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
         spin_unlock(&hb->lock);
 
         /* drops pi_state->pi_mutex.wait_lock */
         ret = wake_futex_pi(uaddr, uval, pi_state);
 
         put_pi_state(pi_state);
 
         /*
          * Success, we're done! No tricky corner cases.
          */
         if (!ret)
             return ret;
         /*
          * The atomic access to the futex value generated a
          * pagefault, so retry the user-access and the wakeup:
          */
         if (ret == -EFAULT)
             goto pi_faulted;
         /*
          * A unconditional UNLOCK_PI op raced against a waiter
          * setting the FUTEX_WAITERS bit. Try again.
          */
         if (ret == -EAGAIN)
             goto pi_retry;
         /*
          * wake_futex_pi has detected invalid state. Tell user
          * space.
          */
         return ret;
     }
 
     /*
      * We have no kernel internal state, i.e. no waiters in the
      * kernel. Waiters which are about to queue themselves are stuck
      * on hb->lock. So we can safely ignore them. We do neither
      * preserve the WAITERS bit not the OWNER_DIED one. We are the
      * owner.
      */
     if ((ret = futex_cmpxchg_value_locked(&curval, uaddr, uval, 0))) {
         spin_unlock(&hb->lock);
         switch (ret) {
         case -EFAULT:
             goto pi_faulted;
 
         case -EAGAIN:
             goto pi_retry;
 
         default:
             WARN_ON_ONCE(1);
             return ret;
         }
     }
 
     /*
      * If uval has changed, let user space handle it.
      */
     ret = (curval == uval) ? 0 : -EAGAIN;
 
 out_unlock:
     spin_unlock(&hb->lock);
     return ret;
 
 pi_retry:
     cond_resched();
     goto retry;
 
 pi_faulted:
 
     ret = fault_in_user_writeable(uaddr);
     if (!ret)
         goto retry;
 
     return ret;
 }
 

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