From: Jens Axboe Date: Thu, 26 Jan 2017 19:50:36 +0000 (-0700) Subject: blk-mq: fix potential race in queue restart and driver tag allocation X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=3c782d67c16889d753a79a8da5422c583d7cfd51;p=openwrt%2Fstaging%2Fblogic.git blk-mq: fix potential race in queue restart and driver tag allocation Once we mark the queue as needing a restart, re-check if we can get a driver tag. This fixes a theoretical issue where the needed IO completes _after_ blk_mq_get_driver_tag() fails, but before we manage to set the restart bit. Signed-off-by: Jens Axboe Reviewed-by: Omar Sandoval Tested-by: Hannes Reinecke --- diff --git a/block/blk-mq.c b/block/blk-mq.c index 1f948d5c2715..fd80101c7591 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -928,8 +928,16 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list) if (!blk_mq_get_driver_tag(rq, &hctx, false)) { if (!queued && reorder_tags_to_front(list)) continue; + + /* + * We failed getting a driver tag. Mark the queue(s) + * as needing a restart. Retry getting a tag again, + * in case the needed IO completed right before we + * marked the queue as needing a restart. + */ blk_mq_sched_mark_restart(hctx); - break; + if (!blk_mq_get_driver_tag(rq, &hctx, false)) + break; } list_del_init(&rq->queuelist);