Darren Hart wrote:
futex_requeue() can acquire the lock on behalf of a waiter during the
requeue
loop in the event of a lock steal or owner died. futex_wait_requeue_pi()
cleans
up the pi_state owner, using the lock_ptr to protect against concurrent
access
to the pi_state. The pi_state is found on the requeue target futex hash
bucket
so the lock_ptr needs to be updated accordingly. The problem manifested by
triggering the WARN_ON in lookup_pi_state() about the pid !=
pi_state->owner
pid.
The astute reviewer will note that still exists a race between the time
futex_requeue() releases hb2->lock() and the time when
futex_wait_requeue_pi()
acquires it. During this time the pi_state and the futex uaddr are not
in sync
with the rt_mutex ownership. This patch closes the window to the point
where
my tests now pass, but we still need to address it.
Note: Please apply to mainline and rt
static inline
-void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
+void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
+ struct futex_hash_bucket *hb)
{
drop_futex_key_refs(&q->key);
get_futex_key_refs(key);
q->key = *key;
+ q->lock_ptr = &hb->lock;
Hrm... turns out changing this breaks the
handle_early_requeue_pi_wakeup() logic. I'll have to respin this patch
to account for that as well. Please hold off on this patch.
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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