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| author | Jens Axboe <jens.axboe@oracle.com> | 2008-12-15 21:19:25 +0100 |
|---|---|---|
| committer | Jens Axboe <jens.axboe@oracle.com> | 2008-12-29 08:29:52 +0100 |
| commit | 62c1fe9d9f0a676fce89185b1513f0e5f473c72c (patch) | |
| tree | 28085a657fa93ed63b7dda20b5a84885e67d429e /block | |
| parent | 8ae30b895805a6e2bb725b1d78b12daabd7eadfe (diff) | |
| download | lwn-62c1fe9d9f0a676fce89185b1513f0e5f473c72c.tar.gz lwn-62c1fe9d9f0a676fce89185b1513f0e5f473c72c.zip | |
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>
Diffstat (limited to 'block')
| -rw-r--r-- | block/cfq-iosched.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index ee8a90c7c46c..e8525fa72823 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -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); } } |