[PATCH V9 1/4] blk-mq: insert to hctx dispatch list when bypass_insert is true

[Jianchao Wang]

We don't allow direct dispatch of anything but regular reads/writes
and insert all of non-read-write requests. However, this is not
correct for 'bypass_insert == true' case where inserting is ignored
and BLK_STS_RESOURCE is returned. The caller will fail forever.

Fix it with inserting the non-read-write request to hctx dispatch
list to avoid to involve merge and io scheduler when bypass_insert
is true.

Signed-off-by: Jianchao Wang <jianchao.w.w...@oracle.com>
---
 block/blk-mq.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9005505..153af90 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1822,6 +1822,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct 
blk_mq_hw_ctx *hctx,
 {
        struct request_queue *q = rq->q;
        bool run_queue = true;
+       bool force = false;
 
        /*
         * RCU or SRCU read lock is needed before checking quiesced flag.
@@ -1836,9 +1837,19 @@ 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_rq_can_direct_dispatch(rq)) {
+               /*
+                * For 'bypass_insert == true' case, insert request into hctx
+                * dispatch list.
+                */
+               if (bypass_insert)
+                       force = true;
+               goto insert;
+       }
+
        if (!blk_mq_get_dispatch_budget(hctx))
                goto insert;
 
@@ -1849,8 +1860,12 @@ static blk_status_t __blk_mq_try_issue_directly(struct 
blk_mq_hw_ctx *hctx,
 
        return __blk_mq_issue_directly(hctx, rq, cookie, last);
 insert:
-       if (bypass_insert)
+       if (force) {
+               blk_mq_request_bypass_insert(rq, run_queue);
+               return BLK_STS_OK;
+       } else if (bypass_insert) {
                return BLK_STS_RESOURCE;
+       }
 
        blk_mq_sched_insert_request(rq, false, run_queue, false);
        return BLK_STS_OK;
-- 
2.7.4