Commit 9b50902d authored Jun 05, 2011 by Jens Axboe

cfq-iosched: fix locking around ioc->ioc_data assignment

Since we are modifying this RCU pointer, we need to hold
the lock protecting it around it.

This fixes a potential reuse and double free of a cfq
io_context structure. The bug has been in CFQ for a long
time, it hit very few people but those it did hit seemed
to see it a lot.

Tracked in RH bugzilla here:

https://bugzilla.redhat.com/show_bug.cgi?id=577968



Credit goes to Paul Bolle for figuring out that the issue
was around the one-hit ioc->ioc_data cache. Thanks to his
hard work the issue is now fixed.

Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

parent 796d5116

block/cfq-iosched.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -2767,8 +2767,11 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
		smp_wmb();
		cic->key = cfqd_dead_key(cfqd);

		if (ioc->ioc_data == cic)
		if (rcu_dereference(ioc->ioc_data) == cic) {
		spin_lock(&ioc->lock);
		rcu_assign_pointer(ioc->ioc_data, NULL);
		spin_unlock(&ioc->lock);
		}

		if (cic->cfqq[BLK_RW_ASYNC]) {
		cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);

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