Commit 62c1fe9d authored Dec 15, 2008 by Jens Axboe

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>

parent 8ae30b89

block/cfq-iosched.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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);

		/*
		* 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);
		}
		}