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cfq-iosched: fix race between exiting queue and exiting task 

Original patch from Nikanth Karthikesan <knikanth@suse.de>

When a queue exits the queue lock is taken and cfq_exit_queue() would free all
the cic's associated with the queue.

But when a task exits, cfq_exit_io_context() gets cic one by one and then
locks the associated queue to call __cfq_exit_single_io_context. It looks like
between getting a cic from the ioc and locking the queue, the queue might have
exited on another cpu.

Fix this by rechecking the cfq_io_context queue key inside the queue lock
again, and not calling into __cfq_exit_single_io_context() if somebody
beat us to it.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-12-15 21:19:25 +01:00
parent 8ae30b8958
commit 62c1fe9d9f
1 changed files with 9 additions and 1 deletions
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10
block/cfq-iosched.c
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@ -1314,7 +1314,15 @@ static void cfq_exit_single_io_context(struct io_context *ioc,
unsigned long flags;
spin_lock_irqsave(q->queue_lock, flags);
__cfq_exit_single_io_context(cfqd, cic);
/*
* Ensure we get a fresh copy of the ->key to prevent
* race between exiting task and queue
*/
smp_read_barrier_depends();
if (cic->key)
__cfq_exit_single_io_context(cfqd, cic);
spin_unlock_irqrestore(q->queue_lock, flags);
}
}