Patch "block: fix hctx checks for batch allocation" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    block: fix hctx checks for batch allocation

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     block-fix-hctx-checks-for-batch-allocation.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b0556c1b65b326c8cf82fdb5d7bacc6a44e57de9
Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
Date:   Tue Jan 17 11:42:15 2023 +0000

    block: fix hctx checks for batch allocation
    
    [ Upstream commit 7746564793978fe2f43b18a302b22dca0ad3a0e8 ]
    
    When there are no read queues read requests will be assigned a
    default queue on allocation. However, blk_mq_get_cached_request() is not
    prepared for that and will fail all attempts to grab read requests from
    the cache. Worst case it doubles the number of requests allocated,
    roughly half of which will be returned by blk_mq_free_plug_rqs().
    
    It only affects batched allocations and so is io_uring specific.
    For reference, QD8 t/io_uring benchmark improves by 20-35%.
    
    Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
    Link: https://lore.kernel.org/r/80d4511011d7d4751b4cf6375c4e38f237d935e3.1673955390.git.asml.silence@xxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 63abbe342b28..83fbc7c54617 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2858,6 +2858,7 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
 		struct blk_plug *plug, struct bio **bio, unsigned int nsegs)
 {
 	struct request *rq;
+	enum hctx_type type, hctx_type;
 
 	if (!plug)
 		return NULL;
@@ -2870,7 +2871,10 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
 		return NULL;
 	}
 
-	if (blk_mq_get_hctx_type((*bio)->bi_opf) != rq->mq_hctx->type)
+	type = blk_mq_get_hctx_type((*bio)->bi_opf);
+	hctx_type = rq->mq_hctx->type;
+	if (type != hctx_type &&
+	    !(type == HCTX_TYPE_READ && hctx_type == HCTX_TYPE_DEFAULT))
 		return NULL;
 	if (op_is_flush(rq->cmd_flags) != op_is_flush((*bio)->bi_opf))
 		return NULL;