linux-kernel - [PATCH AUTOSEL for 4.14 063/135] btrfs: fix false EIO for missing device

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Date:   Thu, 7 Dec 2017 15:45:45 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Anand Jain <anand.jain@...cle.com>,
        David Sterba <dsterba@...e.com>, alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.14 063/135] btrfs: fix false EIO for missing
 device

From: Anand Jain <anand.jain@...cle.com>

[ Upstream commit 102ed2c5ff932439bbbe74c7bd63e6d5baa9f732 ]

When one of the device is missing, bbio_error() takes care of setting
the error status. And if its only IO that is pending in that stripe, it
fails to check the status of the other IO at %bbio_error before setting
the error %bi_status for the %orig_bio. Fix this by checking if
%bbio->error has exceeded the %bbio->max_errors.

Reproducer as below fdatasync error is seen intermittently.

 mount -o degraded /dev/sdc /btrfs
 dd status=none if=/dev/zero of=$(mktemp /btrfs/XXX) bs=4096 count=1 conv=fdatasync

 dd: fdatasync failed for ‘/btrfs/LSe’: Input/output error

 The reason for the intermittences of the problem is because
 the following conditions have to be met, which depends on timing:
 In btrfs_map_bio()
  - the RAID1 the missing device has to be at %dev_nr = 1
 In bbio_error()
  . before bbio_error() is called the bio of the not-missing
    device at %dev_nr = 0 must be completed so that the below
    condition is true
     if (atomic_dec_and_test(&bbio->stripes_pending)) {

Signed-off-by: Anand Jain <anand.jain@...cle.com>
Reviewed-by: Liu Bo <bo.li.liu@...cle.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 fs/btrfs/volumes.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b39737568c22..abc57f7b2716 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6144,7 +6144,10 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
 
 		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		bio->bi_iter.bi_sector = logical >> 9;
-		bio->bi_status = BLK_STS_IOERR;
+		if (atomic_read(&bbio->error) > bbio->max_errors)
+			bio->bi_status = BLK_STS_IOERR;
+		else
+			bio->bi_status = BLK_STS_OK;
 		btrfs_end_bbio(bbio, bio);
 	}
 }
-- 
2.11.0