Messages in this thread Patches in this message | | | From | Nikanth Karthikesan <> | Subject | [PATCH] Exiting queue and task might race to free cic | Date | Wed, 19 Nov 2008 15:27:17 +0530 |
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Hi Jens
Looking at the bug reported here http://thread.gmane.org/gmane.linux.kernel/722539 it looks like an exiting queue can race with an exiting task.
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. Isn't this possible?
If possible, either verifying whether cic->key is still not null or q->flags does not have QUEUE_FLAG_DEAD set would fix this.
Thanks Nikanth Karthikesan
Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
--- diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 6a062ee..b9b627a 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1318,7 +1318,12 @@ 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); + /* + * cic might have been already exited when an exiting task + * races with an exiting queue. + */ + if (likely(cic->key)) + __cfq_exit_single_io_context(cfqd, cic); spin_unlock_irqrestore(q->queue_lock, flags); } } Or this would also work
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 6a062ee..7a068bd 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1318,7 +1318,11 @@ 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); + /* + * Make sure the queue is not dead. + */ + if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) + __cfq_exit_single_io_context(cfqd, cic); spin_unlock_irqrestore(q->queue_lock, flags); } }
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