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authorJens Axboe <jens.axboe@oracle.com>2008-12-15 15:19:25 -0500
committerJens Axboe <jens.axboe@oracle.com>2008-12-29 02:29:52 -0500
commit62c1fe9d9f0a676fce89185b1513f0e5f473c72c (patch)
tree28085a657fa93ed63b7dda20b5a84885e67d429e /block/cfq-iosched.c
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/cfq-iosched.c')
-rw-r--r--block/cfq-iosched.c10
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,
1314 unsigned long flags; 1314 unsigned long flags;
1315 1315
1316 spin_lock_irqsave(q->queue_lock, flags); 1316 spin_lock_irqsave(q->queue_lock, flags);
1317 __cfq_exit_single_io_context(cfqd, cic); 1317
1318 /*
1319 * Ensure we get a fresh copy of the ->key to prevent
1320 * race between exiting task and queue
1321 */
1322 smp_read_barrier_depends();
1323 if (cic->key)
1324 __cfq_exit_single_io_context(cfqd, cic);
1325
1318 spin_unlock_irqrestore(q->queue_lock, flags); 1326 spin_unlock_irqrestore(q->queue_lock, flags);
1319 } 1327 }
1320} 1328}