If blk_poll() is called if no requests are in progress, it may happen that blk_mq_update_nr_hw_queues() modifies the data structures used by blk_poll(), e.g. q->queue_hw_ctx[]. Fix this race by serializing blk_poll() against blk_mq_update_nr_hw_queues().
Cc: Christoph Hellwig <[email protected]> Cc: Ming Lei <[email protected]> Cc: Hannes Reinecke <[email protected]> Cc: Johannes Thumshirn <[email protected]> Signed-off-by: Bart Van Assche <[email protected]> --- block/blk-mq.c | 38 +++++++++++++++++++++++++------------- 1 file changed, 25 insertions(+), 13 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 7528678ef41f..ea64d951f411 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3439,19 +3439,7 @@ static bool blk_mq_poll_hybrid(struct request_queue *q, return blk_mq_poll_hybrid_sleep(q, hctx, rq); } -/** - * blk_poll - poll for IO completions - * @q: the queue - * @cookie: cookie passed back at IO submission time - * @spin: whether to spin for completions - * - * Description: - * Poll for completions on the passed in queue. Returns number of - * completed entries found. If @spin is true, then blk_poll will continue - * looping until at least one completion is found, unless the task is - * otherwise marked running (or we need to reschedule). - */ -int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) +static int __blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) { struct blk_mq_hw_ctx *hctx; long state; @@ -3503,6 +3491,30 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) __set_current_state(TASK_RUNNING); return 0; } + +/** + * blk_poll - poll for IO completions + * @q: the queue + * @cookie: cookie passed back at IO submission time + * @spin: whether to spin for completions + * + * Description: + * Poll for completions on the passed in queue. Returns number of + * completed entries found. If @spin is true, then blk_poll will continue + * looping until at least one completion is found, unless the task is + * otherwise marked running (or we need to reschedule). + */ +int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin) +{ + int ret; + + if (!percpu_ref_tryget(&q->q_usage_counter)) + return 0; + ret = __blk_poll(q, cookie, spin); + blk_queue_exit(q); + + return ret; +} EXPORT_SYMBOL_GPL(blk_poll); unsigned int blk_mq_rq_cpu(struct request *rq) -- 2.23.0.866.gb869b98d4c-goog
