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Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c83
1 files changed, 67 insertions, 16 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 57d0b3657e16..9e69589b9248 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2294,21 +2294,17 @@ static void unqueue_me_pi(struct futex_q *q)
spin_unlock(q->lock_ptr);
}
-/*
- * Fixup the pi_state owner with the new owner.
- *
- * Must be called with hash bucket lock held and mm->sem held for non
- * private futexes.
- */
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *newowner)
+ struct task_struct *argowner)
{
- u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
struct futex_pi_state *pi_state = q->pi_state;
u32 uval, uninitialized_var(curval), newval;
- struct task_struct *oldowner;
+ struct task_struct *oldowner, *newowner;
+ u32 newtid;
int ret;
+ lockdep_assert_held(q->lock_ptr);
+
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
oldowner = pi_state->owner;
@@ -2317,11 +2313,17 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
newtid |= FUTEX_OWNER_DIED;
/*
- * We are here either because we stole the rtmutex from the
- * previous highest priority waiter or we are the highest priority
- * waiter but have failed to get the rtmutex the first time.
+ * We are here because either:
+ *
+ * - we stole the lock and pi_state->owner needs updating to reflect
+ * that (@argowner == current),
*
- * We have to replace the newowner TID in the user space variable.
+ * 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
@@ -2334,6 +2336,42 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
* in the PID check in lookup_pi_state.
*/
retry:
+ if (!argowner) {
+ if (oldowner != current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ ret = 0;
+ goto out_unlock;
+ }
+
+ if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
+ /* We got the lock after all, nothing to fix. */
+ ret = 0;
+ goto out_unlock;
+ }
+
+ /*
+ * Since we just failed the trylock; there must be an owner.
+ */
+ newowner = rt_mutex_owner(&pi_state->pi_mutex);
+ BUG_ON(!newowner);
+ } else {
+ WARN_ON_ONCE(argowner != current);
+ if (oldowner == current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ ret = 0;
+ goto out_unlock;
+ }
+ newowner = argowner;
+ }
+
+ newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+
if (get_futex_value_locked(&uval, uaddr))
goto handle_fault;
@@ -2434,9 +2472,9 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int 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:
*
- * We can safely read pi_state->owner without holding wait_lock
- * because we now own the rt_mutex, only the owner will attempt
- * to change it.
+ * 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)
ret = fixup_pi_state_owner(uaddr, q, current);
@@ -2444,6 +2482,19 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
}
/*
+ * 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) {
+ ret = fixup_pi_state_owner(uaddr, q, NULL);
+ goto out;
+ }
+
+ /*
* Paranoia check. If we did not take the lock, then we should not be
* the owner of the rt_mutex.
*/