From: Ming Lei ming.lei@redhat.com
[ Upstream commit e87eb301bee183d82bb3d04bd71b6660889a2588 ]
Just like aio/io_uring, we need to grab 2 refcount for queuing one request, one is for submission, another is for completion.
If the request isn't queued from plug code path, the refcount grabbed in generic_make_request() serves for submission. In theroy, this refcount should have been released after the sumission(async run queue) is done. blk_freeze_queue() works with blk_sync_queue() together for avoiding race between cleanup queue and IO submission, given async run queue activities are canceled because hctx->run_work is scheduled with the refcount held, so it is fine to not hold the refcount when running the run queue work function for dispatch IO.
However, if request is staggered into plug list, and finally queued from plug code path, the refcount in submission side is actually missed. And we may start to run queue after queue is removed because the queue's kobject refcount isn't guaranteed to be grabbed in flushing plug list context, then kernel oops is triggered, see the following race:
blk_mq_flush_plug_list(): blk_mq_sched_insert_requests() insert requests to sw queue or scheduler queue blk_mq_run_hw_queue
Because of concurrent run queue, all requests inserted above may be completed before calling the above blk_mq_run_hw_queue. Then queue can be freed during the above blk_mq_run_hw_queue().
Fixes the issue by grab .q_usage_counter before calling blk_mq_sched_insert_requests() in blk_mq_flush_plug_list(). This way is safe because the queue is absolutely alive before inserting request.
Cc: Dongli Zhang dongli.zhang@oracle.com Cc: James Smart james.smart@broadcom.com Cc: linux-scsi@vger.kernel.org, Cc: Martin K . Petersen martin.petersen@oracle.com, Cc: Christoph Hellwig hch@lst.de, Cc: James E . J . Bottomley jejb@linux.vnet.ibm.com, Reviewed-by: Bart Van Assche bvanassche@acm.org Tested-by: James Smart james.smart@broadcom.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq-sched.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 0c98b6c1ca49c..1213556a20dad 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -413,6 +413,14 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx, struct list_head *list, bool run_queue_async) { struct elevator_queue *e; + struct request_queue *q = hctx->queue; + + /* + * blk_mq_sched_insert_requests() is called from flush plug + * context only, and hold one usage counter to prevent queue + * from being released. + */ + percpu_ref_get(&q->q_usage_counter);
e = hctx->queue->elevator; if (e && e->type->ops.insert_requests) @@ -426,12 +434,14 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx, if (!hctx->dispatch_busy && !e && !run_queue_async) { blk_mq_try_issue_list_directly(hctx, list); if (list_empty(list)) - return; + goto out; } blk_mq_insert_requests(hctx, ctx, list); }
blk_mq_run_hw_queue(hctx, run_queue_async); + out: + percpu_ref_put(&q->q_usage_counter); }
static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,