linux-kernel - [PATCH AUTOSEL 6.6 08/15] scsi: core: Use GFP_NOIO to avoid circular locking dependency

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Message-Id: <20250211013136.4098219-8-sashal@kernel.org>
Date: Mon, 10 Feb 2025 20:31:28 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Rik van Riel <riel@...riel.com>,
	Marc Aurèle La France <tsi@...oix.net>,
	Christoph Hellwig <hch@....de>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	Sasha Levin <sashal@...nel.org>,
	James.Bottomley@...senPartnership.com,
	linux-scsi@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 08/15] scsi: core: Use GFP_NOIO to avoid circular locking dependency

From: Rik van Riel <riel@...riel.com>

[ Upstream commit 5363ee9d110e139584c2d92a0b640bc210588506 ]

Filesystems can write to disk from page reclaim with __GFP_FS
set. Marc found a case where scsi_realloc_sdev_budget_map() ends up in
page reclaim with GFP_KERNEL, where it could try to take filesystem
locks again, leading to a deadlock.

WARNING: possible circular locking dependency detected
6.13.0 #1 Not tainted
------------------------------------------------------
kswapd0/70 is trying to acquire lock:
ffff8881025d5d78 (&q->q_usage_counter(io)){++++}-{0:0}, at: blk_mq_submit_bio+0x461/0x6e0

but task is already holding lock:
ffffffff81ef5f40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x9f/0x760

The full lockdep splat can be found in Marc's report:

https://lkml.org/lkml/2025/1/24/1101

Avoid the potential deadlock by doing the allocation with GFP_NOIO, which
prevents both filesystem and block layer recursion.

Reported-by: Marc Aurèle La France <tsi@...oix.net>
Signed-off-by: Rik van Riel <riel@...riel.com>
Link: https://lore.kernel.org/r/20250129104525.0ae8421e@fangorn
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/scsi/scsi_scan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index ca99be7341d9b..cead0fbbe5dbd 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -245,7 +245,7 @@ static int scsi_realloc_sdev_budget_map(struct scsi_device *sdev,
 	}
 	ret = sbitmap_init_node(&sdev->budget_map,
 				scsi_device_max_queue_depth(sdev),
-				new_shift, GFP_KERNEL,
+				new_shift, GFP_NOIO,
 				sdev->request_queue->node, false, true);
 	if (!ret)
 		sbitmap_resize(&sdev->budget_map, depth);
-- 
2.39.5