| Message ID | 20250128164700.6d8504c1@fangorn |
|---|---|
| State | New |
| Headers | show |
| Series | scsi: use GFP_NOFS to avoid circular locking dependency | expand |
On Wed, Jan 29, 2025 at 10:45:25AM -0500, Rik van Riel wrote: > On Tue, 28 Jan 2025 21:35:18 -0800 > Christoph Hellwig <hch@infradead.org> wrote: > > > 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. > > Duh, you are right of course! > > The fixed up patch with GFP_NOIO is below. Looks good: Reviewed-by: Christoph Hellwig <hch@lst.de>
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(-)