[PATCH V2 1/2] loop: clear nowait flag in workqueue context

[PATCH V2 1/2] loop: clear nowait flag in workqueue context

[Chaitanya Kulkarni]

The loop driver advertises REQ_NOWAIT support through BLK_FEAT_NOWAIT
(enabled by default for all blk-mq devices), and honors the nowait
behavior throughout loop_queue_rq().

However, actual I/O to the backing file is performed in a workqueue,
where blocking is allowed.

To avoid imposing unnecessary non-blocking constraints in this blocking
context, clear the REQ_NOWAIT flag before processing the request in the
workqueue context.

Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
---

v1->v2:-

Unset REQ_NOWAIT at the start of the workqueue context. (Damien)

HEAD:-

commit 6dbcc40ec7aa17ed3dd1f798e4201e75ab7d7447 (HEAD -> for-next, origin/for-next)
Merge: 58625d626327 ba13710ddd1f
Author: Jens Axboe <axboe@kernel.dk>
Date:   Wed Nov 5 18:24:17 2025 -0700

    Merge branch 'for-6.19/block' into for-next
    
    * for-6.19/block:
      rust: block: update ARef and AlwaysRefCounted imports from sync::aref


---
 drivers/block/loop.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 13ce229d450c..ebe751f39742 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1908,6 +1908,10 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
 		goto failed;
 	}
 
+	/* We can block in this context, so ignore REQ_NOWAIT. */
+	if (rq->cmd_flags & REQ_NOWAIT)
+		rq->cmd_flags &= ~REQ_NOWAIT;
+
 	if (cmd_blkcg_css)
 		kthread_associate_blkcg(cmd_blkcg_css);
 	if (cmd_memcg_css)
-- 
2.40.0

[PATCH V2 2/2] zloop: clear nowait flag in workqueue context

[Chaitanya Kulkarni]

The zloop driver advertises REQ_NOWAIT support through BLK_FEAT_NOWAIT
(enabled by default for all blk-mq devices), and honors the nowait
behavior throughout zloop_queue_rq().

However, actual I/O to the backing file is performed in a workqueue,
where blocking is allowed.

To avoid imposing unnecessary non-blocking constraints in this blocking
context, clear the REQ_NOWAIT flag before processing the request in the
workqueue context.

Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
---

v1->v2:-

Unset REQ_NOWAIT at the start of the workqueue context. (Damien)

HEAD:-

commit 6dbcc40ec7aa17ed3dd1f798e4201e75ab7d7447 (HEAD -> for-next, origin/for-next)
Merge: 58625d626327 ba13710ddd1f
Author: Jens Axboe <axboe@kernel.dk>
Date:   Wed Nov 5 18:24:17 2025 -0700

    Merge branch 'for-6.19/block' into for-next
    
    * for-6.19/block:
      rust: block: update ARef and AlwaysRefCounted imports from sync::aref


---
 drivers/block/zloop.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 92be9f0af00a..1a97b21f5fed 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -498,6 +498,10 @@ static void zloop_handle_cmd(struct zloop_cmd *cmd)
 	struct request *rq = blk_mq_rq_from_pdu(cmd);
 	struct zloop_device *zlo = rq->q->queuedata;
 
+	/* We can block in this context, so ignore REQ_NOWAIT. */
+	if (rq->cmd_flags & REQ_NOWAIT)
+		rq->cmd_flags &= ~REQ_NOWAIT;
+
 	switch (req_op(rq)) {
 	case REQ_OP_READ:
 	case REQ_OP_WRITE:
-- 
2.40.0

Re: [PATCH V2 1/2] loop: clear nowait flag in workqueue context

[Damien Le Moal]

On 11/20/25 8:22 AM, Chaitanya Kulkarni wrote:
> The loop driver advertises REQ_NOWAIT support through BLK_FEAT_NOWAIT
> (enabled by default for all blk-mq devices), and honors the nowait
> behavior throughout loop_queue_rq().
> 
> However, actual I/O to the backing file is performed in a workqueue,
> where blocking is allowed.
> 
> To avoid imposing unnecessary non-blocking constraints in this blocking
> context, clear the REQ_NOWAIT flag before processing the request in the
> workqueue context.
> 
> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH V2 2/2] zloop: clear nowait flag in workqueue context

[Damien Le Moal]

On 11/20/25 8:22 AM, Chaitanya Kulkarni wrote:
> The zloop driver advertises REQ_NOWAIT support through BLK_FEAT_NOWAIT
> (enabled by default for all blk-mq devices), and honors the nowait
> behavior throughout zloop_queue_rq().
> 
> However, actual I/O to the backing file is performed in a workqueue,
> where blocking is allowed.
> 
> To avoid imposing unnecessary non-blocking constraints in this blocking
> context, clear the REQ_NOWAIT flag before processing the request in the
> workqueue context.
> 
> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH V2 1/2] loop: clear nowait flag in workqueue context

[Jens Axboe]

On Wed, 19 Nov 2025 15:22:33 -0800, Chaitanya Kulkarni wrote:
> The loop driver advertises REQ_NOWAIT support through BLK_FEAT_NOWAIT
> (enabled by default for all blk-mq devices), and honors the nowait
> behavior throughout loop_queue_rq().
> 
> However, actual I/O to the backing file is performed in a workqueue,
> where blocking is allowed.
> 
> [...]

Applied, thanks!

[1/2] loop: clear nowait flag in workqueue context
      commit: b11e483a1cc32e7b557ff680e9bfb4ff11dea9c1
[2/2] zloop: clear nowait flag in workqueue context
      commit: e8f0abdd49baacee3886d5827f113514fcd9fd05

Best regards,
-- 
Jens Axboe