linux-kernel - [PATCH RFC v3 01/22] blk-mq: Don't get budget for reserved requests

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Date:   Tue, 25 Oct 2022 18:17:55 +0800
From:   John Garry <john.garry@...wei.com>
To:     <axboe@...nel.dk>, <damien.lemoal@...nsource.wdc.com>,
        <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <jinpu.wang@...ud.ionos.com>, <hare@...e.de>, <bvanassche@....org>,
        <hch@....de>, <ming.lei@...hat.com>, <niklas.cassel@....com>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-ide@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <linuxarm@...wei.com>, John Garry <john.garry@...wei.com>
Subject: [PATCH RFC v3 01/22] blk-mq: Don't get budget for reserved requests

It should be possible to send reserved requests even when there is no
budget, so don't request a budget in that case.

This comes into play when we need to allocate a reserved request from the
target device request queue for error handling for that same device.

Signed-off-by: John Garry <john.garry@...wei.com>
---
 block/blk-mq.c          | 4 +++-
 drivers/scsi/scsi_lib.c | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 260adeb2e455..d8baabb32ea4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1955,11 +1955,13 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 	errors = queued = 0;
 	do {
 		struct blk_mq_queue_data bd;
+		bool need_budget;
 
 		rq = list_first_entry(list, struct request, queuelist);
 
 		WARN_ON_ONCE(hctx != rq->mq_hctx);
-		prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);
+		need_budget = !nr_budgets && !blk_mq_is_reserved_rq(rq);
+		prep = blk_mq_prep_dispatch_rq(rq, need_budget);
 		if (prep != PREP_DISPATCH_OK)
 			break;
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index fa96d3cfdfa3..39d4fd124375 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -298,7 +298,8 @@ void scsi_device_unbusy(struct scsi_device *sdev, struct scsi_cmnd *cmd)
 	if (starget->can_queue > 0)
 		atomic_dec(&starget->target_busy);
 
-	sbitmap_put(&sdev->budget_map, cmd->budget_token);
+	if (!blk_mq_is_reserved_rq(scsi_cmd_to_rq(cmd)))
+		sbitmap_put(&sdev->budget_map, cmd->budget_token);
 	cmd->budget_token = -1;
 }
 
-- 
2.35.3