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From:   NeilBrown <neilb@suse.com>
To:     Shaohua Li <shli@kernel.org>
Date:   Thu, 26 Apr 2018 14:46:29 +1000
Cc:     Goldwyn Rodrigues <rgoldwyn@suse.de>
Subject: [PATCH] md: fix two problems with setting the "re-add" device state.
cc:     Linux RAID Mailing List <linux-raid@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Message-ID: <87efj2mv6i.fsf@notabene.neil.brown.name>
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If "re-add" is written to the "state" file for a device
which is faulty, this has an effect similar to removing
and re-adding the device.  It should take up the
same slot in the array that it previously had, and
an accelerated (e.g. bitmap-based) rebuild should happen.

The slot that "it previously had" is determined by
rdev->saved_raid_disk.
However this is not set when a device fails (only when a device
is added), and it is cleared when resync completes.
This means that "re-add" will normally work once, but may not work a
second time.

This patch includes two fixes.
1/ when a device fails, record the ->raid_disk value in
    ->saved_raid_disk before clearing ->raid_disk
2/ when "re-add" is written to a device for which
    ->saved_raid_disk is not set, fail.

I think this is suitable for stable as it can
cause re-adding a device to be forced to do a full
resync which takes a lot longer and so puts data at
more risk.

Cc: <stable@vger.kernel.org> (v4.1)
Fixes: 97f6cd39da22 ("md-cluster: re-add capabilities")
Signed-off-by: NeilBrown <neilb@suse.com>
=2D--
 drivers/md/md.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3bea45e8ccff..ecd4235c6e30 100644
=2D-- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2853,7 +2853,8 @@ state_store(struct md_rdev *rdev, const char *buf, si=
ze_t len)
 			err =3D 0;
 		}
 	} else if (cmd_match(buf, "re-add")) {
=2D		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk =3D=3D -1)) {
+		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk =3D=3D -1) &&
+			rdev->saved_raid_disk >=3D 0) {
 			/* clear_bit is performed _after_ all the devices
 			 * have their local Faulty bit cleared. If any writes
 			 * happen in the meantime in the local node, they
@@ -8641,6 +8642,7 @@ static int remove_and_add_spares(struct mddev *mddev,
 			if (mddev->pers->hot_remove_disk(
 				    mddev, rdev) =3D=3D 0) {
 				sysfs_unlink_rdev(mddev, rdev);
+				rdev->saved_raid_disk =3D rdev->raid_disk;
 				rdev->raid_disk =3D -1;
 				removed++;
 			}
=2D-=20
2.14.0.rc0.dirty


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