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Date: Wed, 05 Aug 2009 22:15:03 -0700 From: Darren Hart <dvhltc@...ibm.com> To: linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org CC: tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, mingo@...e.hu, dino@...ibm.com, johnstul@...ibm.com, John Kacur <jkacur@...hat.com> Subject: Re: [PATCH 1/2] Update woken requeued futex_q lock_ptr 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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