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authorVivek Goyal <vgoyal@redhat.com>2011-05-19 15:38:22 -0400
committerJens Axboe <jaxboe@fusionio.com>2011-05-20 20:34:52 +0200
commit56edf7d75db5b14d628b46623c414ffbeed68d7f (patch)
tree7d7ff46f03676154d0edf3da85c8e738d506ad92 /block/blk-core.c
parent3e59cf9d66a87763fef6c232a4a8dc664461ca50 (diff)
cfq-iosched: Fix a possible race with cfq cgroup removal code
blkg->key = cfqd is an rcu protected pointer and hence we used to do call_rcu(cfqd->rcu_head) to free up cfqd after one rcu grace period. The problem here is that even though cfqd is around, there are no gurantees that associated request queue (td->queue) or q->queue_lock is still around. A driver might have called blk_cleanup_queue() and release the lock. It might happen that after freeing up the lock we call blkg->key->queue->queue_ock and crash. This is possible in following path. blkiocg_destroy() blkio_unlink_group_fn() cfq_unlink_blkio_group() Hence, wait for an rcu peirod if there are groups which have not been unlinked from blkcg->blkg_list. That way, if there are any groups which are taking cfq_unlink_blkio_group() path, can safely take queue lock. This is how we have taken care of race in throttling logic also. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'block/blk-core.c')
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