Filesystems can write to disk from page reclaim with filesystem
locks held, if __GFP_FS is 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_NOFS.
Reported-by: Marc Aurèle La France <tsi@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
---
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 f2093982b3db..93d6feef9c7c 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_NOFS,
sdev->request_queue->node, false, true);
if (!ret)
sbitmap_resize(&sdev->budget_map, depth);
--
2.47.1
