Re: [PATCH] nvme: don't call blk_mq_{,un}quiesce_tagset when ctrl->tagset is NULL

[Christoph Hellwig <hch@lst.de>]

On Tue, Nov 22, 2022 at 01:31:54PM +0100, Christoph Hellwig wrote:
> This would be the queue_count version.  I have to say I much prefer
> the tagset check, as it is self-documenting and matches what
> nvme_queue_scan, nvme_cancel_tagset and nvme_cancel_admin_tagset
> do.

And here is the actual patch:

---
From 167d14d9613014142ee285c2912dadc089d80e86 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Wed, 16 Nov 2022 08:14:46 +0100
Subject: nvme: don't call blk_mq_{,un}quiesce_tagset when ctrl->tagset is NULL

The NVMe drivers support a mode where no tagset is allocated for the I/O
queues and only the admin queue is usable.  In that case
ctrl->queue_count is smaller than two and we must not call the block
per-tagset quiesce helpers that dereference it.

Fixes: 98d81f0df70c ("nvme: use blk_mq_[un]quiesce_tagset")
Reported-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 3195ae17df309..6c8a110d6738a 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -5215,6 +5215,8 @@ EXPORT_SYMBOL_GPL(nvme_start_freeze);
 
 void nvme_quiesce_io_queues(struct nvme_ctrl *ctrl)
 {
+	if (ctrl->queue_count < 2)
+		return;
 	if (!test_and_set_bit(NVME_CTRL_STOPPED, &ctrl->flags))
 		blk_mq_quiesce_tagset(ctrl->tagset);
 	else
@@ -5224,6 +5226,8 @@ EXPORT_SYMBOL_GPL(nvme_quiesce_io_queues);
 
 void nvme_unquiesce_io_queues(struct nvme_ctrl *ctrl)
 {
+	if (ctrl->queue_count < 2)
+		return;
 	if (test_and_clear_bit(NVME_CTRL_STOPPED, &ctrl->flags))
 		blk_mq_unquiesce_tagset(ctrl->tagset);
 }
-- 
2.30.2