From b1ad9117b692986f2fc0d2d1b3f6f56b696d38cc Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Sun, 5 Jun 2011 06:01:13 +0200 Subject: [PATCH] cfq-iosched: fix locking around ioc->ioc_data assignment commit ab4bd22d3cce6977dc039664cc2d052e3147d662 upstream. 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. Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/cfq-iosched.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index ab7a9e6a9b1c..d31adc2c9513 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -2704,8 +2704,11 @@ 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]); -- 2.39.5