From: Jens Axboe Date: Sun, 5 Jun 2011 04:01:13 +0000 (+0200) Subject: cfq-iosched: fix locking around ioc->ioc_data assignment X-Git-Tag: v2.6.34.12~93 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=470564b1d4c27fd2bafc421acf49718bfcf5ea5a;p=karo-tx-linux.git 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: Paul Gortmaker --- diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 4fab7c9df71d..510552a4bde2 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -2559,8 +2559,11 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd, cic->dead_key = (unsigned long) cic->key; cic->key = NULL; - 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]);