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>
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@ -2772,8 +2772,11 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
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smp_wmb();
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cic->key = cfqd_dead_key(cfqd);
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if (ioc->ioc_data == cic)
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if (rcu_dereference(ioc->ioc_data) == cic) {
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spin_lock(&ioc->lock);
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rcu_assign_pointer(ioc->ioc_data, NULL);
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spin_unlock(&ioc->lock);
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}
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if (cic->cfqq[BLK_RW_ASYNC]) {
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cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
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