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| author | Akinobu Mita <akinobu.mita@gmail.com> | 2015-09-27 02:09:25 +0900 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2015-09-29 11:32:51 -0600 |
| commit | 60de074ba1e8f327db19bc33d8530131ac01695d (patch) | |
| tree | b23080dbac15be404a4c47da9d83ec7b83cbd3f7 /block/blk-mq.c | |
| parent | 5778322e67ed34dc9f391a4a5cbcbb856071ceba (diff) | |
blk-mq: fix deadlock when reading cpu_list
CPU hotplug handling for blk-mq (blk_mq_queue_reinit) acquires
all_q_mutex in blk_mq_queue_reinit_notify() and then removes sysfs
entries by blk_mq_sysfs_unregister(). Removing sysfs entry needs to
be blocked until the active reference of the kernfs_node to be zero.
On the other hand, reading blk_mq_hw_sysfs_cpu sysfs entry (e.g.
/sys/block/nullb0/mq/0/cpu_list) acquires all_q_mutex in
blk_mq_hw_sysfs_cpus_show().
If these happen at the same time, a deadlock can happen. Because one
can wait for the active reference to be zero with holding all_q_mutex,
and the other tries to acquire all_q_mutex with holding the active
reference.
The reason that all_q_mutex is acquired in blk_mq_hw_sysfs_cpus_show()
is to avoid reading an imcomplete hctx->cpumask. Since reading sysfs
entry for blk-mq needs to acquire q->sysfs_lock, we can avoid deadlock
and reading an imcomplete hctx->cpumask by protecting q->sysfs_lock
while hctx->cpumask is being updated.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
| -rw-r--r-- | block/blk-mq.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index a5dbd069c9da..31c0c6259c4c 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1797,6 +1797,11 @@ static void blk_mq_map_swqueue(struct request_queue *q, struct blk_mq_ctx *ctx; struct blk_mq_tag_set *set = q->tag_set; + /* + * Avoid others reading imcomplete hctx->cpumask through sysfs + */ + mutex_lock(&q->sysfs_lock); + queue_for_each_hw_ctx(q, hctx, i) { cpumask_clear(hctx->cpumask); hctx->nr_ctx = 0; @@ -1816,6 +1821,8 @@ static void blk_mq_map_swqueue(struct request_queue *q, hctx->ctxs[hctx->nr_ctx++] = ctx; } + mutex_unlock(&q->sysfs_lock); + queue_for_each_hw_ctx(q, hctx, i) { struct blk_mq_ctxmap *map = &hctx->ctx_map; |