path: root/block
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authorJens Axboe <jens.axboe@oracle.com>2008-12-15 21:19:25 +0100
committerJens Axboe <jens.axboe@oracle.com>2008-12-29 08:29:52 +0100
commit62c1fe9d9f0a676fce89185b1513f0e5f473c72c (patch)
tree28085a657fa93ed63b7dda20b5a84885e67d429e /block
parent8ae30b895805a6e2bb725b1d78b12daabd7eadfe (diff)
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')
1 files changed, 9 insertions, 1 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ee8a90c7c46..e8525fa7282 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);