diff options
| author | Ming Lei <ming.lei@redhat.com> | 2020-08-17 18:01:15 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-09-03 11:27:01 +0200 |
| commit | b1a83ee0cbbf168c41be3e6a1c8cf045eeca07a1 (patch) | |
| tree | a384a7559460a1a820561d57b08b6395f74af345 /block/blk-mq.c | |
| parent | c2035d1e55aa3e005fe9ca5f15f56398575b44cb (diff) | |
blk-mq: order adding requests to hctx->dispatch and checking SCHED_RESTART
commit d7d8535f377e9ba87edbf7fbbd634ac942f3f54f upstream.
SCHED_RESTART code path is relied to re-run queue for dispatch requests
in hctx->dispatch. Meantime the SCHED_RSTART flag is checked when adding
requests to hctx->dispatch.
memory barriers have to be used for ordering the following two pair of OPs:
1) adding requests to hctx->dispatch and checking SCHED_RESTART in
blk_mq_dispatch_rq_list()
2) clearing SCHED_RESTART and checking if there is request in hctx->dispatch
in blk_mq_sched_restart().
Without the added memory barrier, either:
1) blk_mq_sched_restart() may miss requests added to hctx->dispatch meantime
blk_mq_dispatch_rq_list() observes SCHED_RESTART, and not run queue in
dispatch side
or
2) blk_mq_dispatch_rq_list still sees SCHED_RESTART, and not run queue
in dispatch side, meantime checking if there is request in
hctx->dispatch from blk_mq_sched_restart() is missed.
IO hang in ltp/fs_fill test is reported by kernel test robot:
https://lkml.org/lkml/2020/7/26/77
Turns out it is caused by the above out-of-order OPs. And the IO hang
can't be observed any more after applying this patch.
Fixes: bd166ef183c2 ("blk-mq-sched: add framework for MQ capable IO schedulers")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Jeffery <djeffery@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'block/blk-mq.c')
| -rw-r--r-- | block/blk-mq.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index 8f67f0f16ec2..b748d1e63f9c 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1319,6 +1319,15 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, spin_unlock(&hctx->lock); /* + * Order adding requests to hctx->dispatch and checking + * SCHED_RESTART flag. The pair of this smp_mb() is the one + * in blk_mq_sched_restart(). Avoid restart code path to + * miss the new added requests to hctx->dispatch, meantime + * SCHED_RESTART is observed here. + */ + smp_mb(); + + /* * If SCHED_RESTART was set by the caller of this function and * it is no longer set that means that it was cleared by another * thread and hence that a queue rerun is needed. |