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[topic/core-for-CI] scsi: use GFP_NOIO to avoid circular locking dependency

Message ID 20250204024719.1336311-1-lucas.demarchi@intel.com (mailing list archive)
State New
Headers show
Series [topic/core-for-CI] scsi: use GFP_NOIO to avoid circular locking dependency | expand

Commit Message

Lucas De Marchi Feb. 4, 2025, 2:47 a.m. UTC 
From: Rik van Riel <riel@surriel.com>

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@tuyoix.net>
Signed-off-by: Rik van Riel <riel@surriel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
---
 drivers/scsi/scsi_scan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 087fcbfc9aaa3..96d7e1a9a7c7a 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -246,7 +246,7 @@  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);