[PATCH] md/raid5: fix soft lockup in retry_aligned_read()

[Chia-Ming Chang <chiamingc@synology.com>]

When retry_aligned_read() encounters an overlapped stripe, it releases
the stripe via raid5_release_stripe() which puts it on the lockless
released_stripes llist. In the next raid5d loop iteration,
release_stripe_list() drains the stripe onto handle_list (since
STRIPE_HANDLE is set by the original IO), but retry_aligned_read()
runs before handle_active_stripes() and removes the stripe from
handle_list via find_get_stripe() -> list_del_init(). This prevents
handle_stripe() from ever processing the stripe to resolve the
overlap, causing an infinite loop and soft lockup.

Fix this by using __release_stripe() with temp_inactive_list instead
of raid5_release_stripe() in the failure path, so the stripe does not
go through the released_stripes llist. This allows raid5d to break out
of its loop, and the overlap will be resolved when the stripe is
eventually processed by handle_stripe().

Fixes: 773ca82fa1ee ("raid5: make release_stripe lockless")
Cc: stable@vger.kernel.org
Signed-off-by: FengWei Shih <dannyshih@synology.com>
Signed-off-by: Chia-Ming Chang <chiamingc@synology.com>
---
 drivers/md/raid5.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index a8e8d431071b..335d2b6b1079 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6641,7 +6641,13 @@ static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio,
 		}
 
 		if (!add_stripe_bio(sh, raid_bio, dd_idx, 0, 0)) {
-			raid5_release_stripe(sh);
+			int hash;
+
+			spin_lock_irq(&conf->device_lock);
+			hash = sh->hash_lock_index;
+			__release_stripe(conf, sh,
+					 &conf->temp_inactive_list[hash]);
+			spin_unlock_irq(&conf->device_lock);
 			conf->retry_read_aligned = raid_bio;
 			conf->retry_read_offset = scnt;
 			return handled;
-- 
2.34.1


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