| Message ID | 20250128164700.6d8504c1@fangorn (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | scsi: use GFP_NOFS to avoid circular locking dependency | expand |
GFP_NOFS is never the right thing for block layer allocations. The right thing here is GFP_NOIO which is a superset of GFP_NOFS. Otherwise you could reproduce the same deadlock when using swap instead of a file system to reproduce basically the same deadlock. Note that this: https://lore.kernel.org/linux-block/20250117074442.256705-3-hch@lst.de/T/#u should probably fix the actual deadlock, but it might still need annotations for lockdep to deal with the initial probing where the queue is not frozen. Compared to hacky annotations just using GFP_NOIO feels simpler and more obvious.
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);
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@tuyoix.net> Signed-off-by: Rik van Riel <riel@surriel.com> --- drivers/scsi/scsi_scan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)