[PATCH 4/6] blk-mq: decide how to handle flush rq via RQF_FLUSH_SEQ

[Ming Lei]

Now we always preallocate one driver tag before blk_insert_flush(),
and flush request will be marked as RQF_FLUSH_SEQ once it is in
flush machinary.

So if RQF_FLUSH_SEQ isn't set, we call blk_insert_flush()
to handle the request, otherwise the flush request is
dispatched to ->dispatch list directly.

This is a prepare patch for not preallocating driver tag
on flush rq, and remove the special case.

Signed-off-by: Ming Lei <ming....@redhat.com>
---
 block/blk-mq-sched.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 4ab69435708c..b6399d99438e 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -260,21 +260,22 @@ void blk_mq_sched_request_inserted(struct request *rq)
 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 
 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
+                                      bool has_sched,
                                       struct request *rq)
 {
-       if (rq->tag == -1) {
-               rq->rq_flags |= RQF_SORTED;
-               return false;
+       /* dispatch flush rq directly */
+       if (rq->rq_flags & RQF_FLUSH_SEQ) {
+               spin_lock(&hctx->lock);
+               list_add(&rq->queuelist, &hctx->dispatch);
+               spin_unlock(&hctx->lock);
+               return true;
        }
 
-       /*
-        * If we already have a real request tag, send directly to
-        * the dispatch list.
-        */
-       spin_lock(&hctx->lock);
-       list_add(&rq->queuelist, &hctx->dispatch);
-       spin_unlock(&hctx->lock);
-       return true;
+       WARN_ON(rq->tag != -1);
+       if (has_sched)
+               rq->rq_flags |= RQF_SORTED;
+
+       return false;
 }
 
 /**
@@ -362,12 +363,13 @@ void blk_mq_sched_insert_request(struct request *rq, bool 
at_head,
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
 
-       if (rq->tag == -1 && op_is_flush(rq->cmd_flags)) {
+       /* flush rq in flush machinery need to be dispatched directly */
+       if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
                blk_mq_sched_insert_flush(hctx, rq, can_block);
                return;
        }
 
-       if (e && blk_mq_sched_bypass_insert(hctx, rq))
+       if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
                goto run;
 
        if (e && e->type->ops.mq.insert_requests) {
@@ -405,7 +407,7 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
                list_for_each_entry_safe(rq, next, list, queuelist) {
                        if (WARN_ON_ONCE(rq->tag != -1)) {
                                list_del_init(&rq->queuelist);
-                               blk_mq_sched_bypass_insert(hctx, rq);
+                               blk_mq_sched_bypass_insert(hctx, true, rq);
                        }
                }
        }
-- 
2.9.5