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authorJens Axboe <axboe@kernel.dk>2018-12-06 22:17:44 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-12-08 12:59:10 +0100
commit55cbeea76e769b12cd0f1340132d32781f73a3dc (patch)
parent6235c229fea4e5c5fb35002a5ee1ae2dc65d3198 (diff)
blk-mq: punt failed direct issue to dispatch list
commit c616cbee97aed4bc6178f148a7240206dcdb85a6 upstream. After the direct dispatch corruption fix, we permanently disallow direct dispatch of non read/write requests. This works fine off the normal IO path, as they will be retried like any other failed direct dispatch request. But for the blk_insert_cloned_request() that only DM uses to bypass the bottom level scheduler, we always first attempt direct dispatch. For some types of requests, that's now a permanent failure, and no amount of retrying will make that succeed. This results in a livelock. Instead of making special cases for what we can direct issue, and now having to deal with DM solving the livelock while still retaining a BUSY condition feedback loop, always just add a request that has been through ->queue_rq() to the hardware queue dispatch list. These are safe to use as no merging can take place there. Additionally, if requests do have prepped data from drivers, we aren't dependent on them not sharing space in the request structure to safely add them to the IO scheduler lists. This basically reverts ffe81d45322c and is based on a patch from Ming, but with the list insert case covered as well. Fixes: ffe81d45322c ("blk-mq: fix corruption with direct issue") Cc: stable@vger.kernel.org Suggested-by: Ming Lei <ming.lei@redhat.com> Reported-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Ming Lei <ming.lei@redhat.com> Acked-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 5 insertions, 28 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d020fffbbcc6..23a53b67cf0d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1698,15 +1698,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
- /*
- * If direct dispatch fails, we cannot allow any merging on
- * this IO. Drivers (like SCSI) may have set up permanent state
- * for this request, like SG tables and mappings, and if we
- * merge to it later on then we'll still only do IO to the
- * original part.
- */
- rq->cmd_flags |= REQ_NOMERGE;
blk_mq_update_dispatch_busy(hctx, true);
@@ -1719,18 +1710,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
return ret;
- * Don't allow direct dispatch of anything but regular reads/writes,
- * as some of the other commands can potentially share request space
- * with data we need for the IO scheduler. If we attempt a direct dispatch
- * on those and fail, we can't safely add it to the scheduler afterwards
- * without potentially overwriting data that the driver has already written.
- */
-static bool blk_rq_can_direct_dispatch(struct request *rq)
- return req_op(rq) == REQ_OP_READ || req_op(rq) == REQ_OP_WRITE;
static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
struct request *rq,
blk_qc_t *cookie,
@@ -1752,7 +1731,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
goto insert;
- if (!blk_rq_can_direct_dispatch(rq) || (q->elevator && !bypass_insert))
+ if (q->elevator && !bypass_insert)
goto insert;
if (!blk_mq_get_dispatch_budget(hctx))
@@ -1768,7 +1747,7 @@ insert:
if (bypass_insert)
- blk_mq_sched_insert_request(rq, false, run_queue, false);
+ blk_mq_request_bypass_insert(rq, run_queue);
return BLK_STS_OK;
@@ -1784,7 +1763,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
- blk_mq_sched_insert_request(rq, false, true, false);
+ blk_mq_request_bypass_insert(rq, true);
else if (ret != BLK_STS_OK)
blk_mq_end_request(rq, ret);
@@ -1814,15 +1793,13 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
struct request *rq = list_first_entry(list, struct request,
- if (!blk_rq_can_direct_dispatch(rq))
- break;
ret = blk_mq_request_issue_directly(rq);
if (ret != BLK_STS_OK) {
if (ret == BLK_STS_RESOURCE ||
- list_add(&rq->queuelist, list);
+ blk_mq_request_bypass_insert(rq,
+ list_empty(list));
blk_mq_end_request(rq, ret);