linux-kernel - [PATCH 3.16 80/83] md/raid: raid5 preserve the writeback action after the parity check

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Message-ID: <lsq.1574264230.785481722@decadent.org.uk>
Date:   Wed, 20 Nov 2019 15:38:30 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Song Liu" <songliubraving@...com>,
        "Nigel Croxon" <ncroxon@...hat.com>
Subject: [PATCH 3.16 80/83] md/raid: raid5 preserve the writeback action
 after the parity check

3.16.78-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nigel Croxon <ncroxon@...hat.com>

commit b2176a1dfb518d870ee073445d27055fea64dfb8 upstream.

The problem is that any 'uptodate' vs 'disks' check is not precise
in this path. Put a "WARN_ON(!test_bit(R5_UPTODATE, &dev->flags)" on the
device that might try to kick off writes and then skip the action.
Better to prevent the raid driver from taking unexpected action *and* keep
the system alive vs killing the machine with BUG_ON.

Note: fixed warning reported by kbuild test robot <lkp@...el.com>

Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Nigel Croxon <ncroxon@...hat.com>
Signed-off-by: Song Liu <songliubraving@...com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/md/raid5.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3385,7 +3385,7 @@ static void handle_parity_checks6(struct
 		/* now write out any block on a failed drive,
 		 * or P or Q if they were recomputed
 		 */
-		BUG_ON(s->uptodate < disks - 1); /* We don't need Q to recover */
+		dev = NULL;
 		if (s->failed == 2) {
 			dev = &sh->dev[s->failed_num[1]];
 			s->locked++;
@@ -3410,6 +3410,14 @@ static void handle_parity_checks6(struct
 			set_bit(R5_LOCKED, &dev->flags);
 			set_bit(R5_Wantwrite, &dev->flags);
 		}
+		if (WARN_ONCE(dev && !test_bit(R5_UPTODATE, &dev->flags),
+			      "%s: disk%td not up to date\n",
+			      mdname(conf->mddev),
+			      dev - (struct r5dev *) &sh->dev)) {
+			clear_bit(R5_LOCKED, &dev->flags);
+			clear_bit(R5_Wantwrite, &dev->flags);
+			s->locked--;
+		}
 		clear_bit(STRIPE_DEGRADED, &sh->state);
 
 		set_bit(STRIPE_INSYNC, &sh->state);