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Subject[PATCH V11 1/4] blk-mq: insert to hctx dispatch list when bypass_insert is true
Date
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.wang@oracle.com>
---
block/blk-mq.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9005505..01802bf 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 +1837,18 @@ 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.
+ */
+ force = bypass_insert;
+ goto insert;
+ }
+
if (!blk_mq_get_dispatch_budget(hctx))
goto insert;

@@ -1849,8 +1859,12 @@ 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
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