Patch "btrfs: fix false EIO for missing device" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

btrfs: fix false EIO for missing device

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-false-eio-for-missing-device.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Anand Jain <[email protected]>
Date: Sat, 14 Oct 2017 08:34:02 +0800
Subject: btrfs: fix false EIO for missing device

From: Anand Jain <[email protected]>

[ 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)) {

---
 fs/btrfs/volumes.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -6144,7 +6144,10 @@ static void bbio_error(struct btrfs_bio
 
 		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);
 	}
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/btrfs-undo-writable-superblocke-when-sprouting-fails.patch queue-4.14/btrfs-fix-false-eio-for-missing-device.patch