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blk-mq: fix race between updating nr_hw_queues and switching io sched

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[ Upstream commit fb350e0ad99359768e1e80b4784692031ec340e4 ]

In both elevator_switch_mq() and blk_mq_update_nr_hw_queues(), sched tags
can be allocated, and q->nr_hw_queue is used, and race is inevitable, for
example: blk_mq_init_sched() may trigger use-after-free on hctx, which is
freed in blk_mq_realloc_hw_ctxs() when nr_hw_queues is decreased.

This patch fixes the race be holding q->sysfs_lock.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ming Lei 2018-01-06 16:27:40 +08:00 committed by Greg Kroah-Hartman
parent eaa077800f
commit fb1ef85d58
1 changed files with 4 additions and 0 deletions
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4
block/blk-mq.c
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@ -2314,6 +2314,9 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
blk_mq_sysfs_unregister(q);
/* protect against switching io scheduler */
mutex_lock(&q->sysfs_lock);
for (i = 0; i < set->nr_hw_queues; i++) {
int node;
@ -2358,6 +2361,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
}
}
q->nr_hw_queues = i;
mutex_unlock(&q->sysfs_lock);
blk_mq_sysfs_register(q);
}