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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-sysfs.c | |
| parent | 5778322e67ed34dc9f391a4a5cbcbb856071ceba (diff) | |
| download | linux-0-day-60de074ba1e8f327db19bc33d8530131ac01695d.tar.gz linux-0-day-60de074ba1e8f327db19bc33d8530131ac01695d.tar.xz | |
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-sysfs.c')
| -rw-r--r-- | block/blk-mq-sysfs.c | 4 |
1 files changed, 0 insertions, 4 deletions
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 189f5ae6522af..788fffd9b4098 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -229,8 +229,6 @@ static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page) unsigned int i, first = 1; ssize_t ret = 0; - blk_mq_disable_hotplug(); - for_each_cpu(i, hctx->cpumask) { if (first) ret += sprintf(ret + page, "%u", i); @@ -240,8 +238,6 @@ static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page) first = 0; } - blk_mq_enable_hotplug(); - ret += sprintf(ret + page, "\n"); return ret; } |