| Date | Sun, 05 Feb 2012 23:10:17 +0100 | From | Willy Tarreau <> | Subject | [PATCH 28/91] cfq-iosched: fix locking around ioc->ioc_data assignment |
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2.6.27-longterm review patch. If anyone has any objections, please let us know.
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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 <jaxboe@fusionio.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> --- block/cfq-iosched.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-)
Index: longterm-2.6.27/block/cfq-iosched.c =================================================================== --- longterm-2.6.27.orig/block/cfq-iosched.c 2012-02-05 22:34:34.185915429 +0100 +++ longterm-2.6.27/block/cfq-iosched.c 2012-02-05 22:34:38.850917663 +0100 @@ -1286,8 +1286,11 @@ 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[ASYNC]) { cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);
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