Commit 1de47f3c authored by Linus Torvalds's avatar Linus Torvalds

Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull  locking fixes from Thomas Gleixner:
 "Two fixes for locking:

   - Plug a hole the pi_stat->owner serialization which was changed
     recently and failed to fixup two usage sites.

   - Prevent reordering of the rwsem_has_spinner() check vs the
     decrement of rwsem count in up_write() which causes a missed
     wakeup"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/rwsem-xadd: Fix missed wakeup due to reordering of load
  futex: Fix pi_state->owner serialization
parents 3d9d62b9 9c29c318
......@@ -821,8 +821,6 @@ static void get_pi_state(struct futex_pi_state *pi_state)
/*
* Drops a reference to the pi_state object and frees or caches it
* when the last reference is gone.
*
* Must be called with the hb lock held.
*/
static void put_pi_state(struct futex_pi_state *pi_state)
{
......@@ -837,16 +835,22 @@ static void put_pi_state(struct futex_pi_state *pi_state)
* and has cleaned up the pi_state already
*/
if (pi_state->owner) {
raw_spin_lock_irq(&pi_state->owner->pi_lock);
list_del_init(&pi_state->list);
raw_spin_unlock_irq(&pi_state->owner->pi_lock);
struct task_struct *owner;
rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
owner = pi_state->owner;
if (owner) {
raw_spin_lock(&owner->pi_lock);
list_del_init(&pi_state->list);
raw_spin_unlock(&owner->pi_lock);
}
rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
}
if (current->pi_state_cache)
if (current->pi_state_cache) {
kfree(pi_state);
else {
} else {
/*
* pi_state->list is already empty.
* clear pi_state->owner.
......@@ -907,13 +911,14 @@ void exit_pi_state_list(struct task_struct *curr)
raw_spin_unlock_irq(&curr->pi_lock);
spin_lock(&hb->lock);
raw_spin_lock_irq(&curr->pi_lock);
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
raw_spin_lock(&curr->pi_lock);
/*
* We dropped the pi-lock, so re-check whether this
* task still owns the PI-state:
*/
if (head->next != next) {
raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
continue;
}
......@@ -922,9 +927,10 @@ void exit_pi_state_list(struct task_struct *curr)
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
pi_state->owner = NULL;
raw_spin_unlock_irq(&curr->pi_lock);
raw_spin_unlock(&curr->pi_lock);
get_pi_state(pi_state);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
rt_mutex_futex_unlock(&pi_state->pi_mutex);
......@@ -1208,6 +1214,10 @@ static int attach_to_pi_owner(u32 uval, union futex_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;
raw_spin_unlock_irq(&p->pi_lock);
......@@ -2878,6 +2888,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
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);
......
......@@ -612,6 +612,33 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
unsigned long flags;
DEFINE_WAKE_Q(wake_q);
/*
* __rwsem_down_write_failed_common(sem)
* rwsem_optimistic_spin(sem)
* osq_unlock(sem->osq)
* ...
* atomic_long_add_return(&sem->count)
*
* - VS -
*
* __up_write()
* if (atomic_long_sub_return_release(&sem->count) < 0)
* rwsem_wake(sem)
* osq_is_locked(&sem->osq)
*
* And __up_write() must observe !osq_is_locked() when it observes the
* atomic_long_add_return() in order to not miss a wakeup.
*
* This boils down to:
*
* [S.rel] X = 1 [RmW] r0 = (Y += 0)
* MB RMB
* [RmW] Y += 1 [L] r1 = X
*
* exists (r0=1 /\ r1=0)
*/
smp_rmb();
/*
* If a spinner is present, it is not necessary to do the wakeup.
* Try to do wakeup only if the trylock succeeds to minimize
......
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