[3.13.y-ckt stable] Patch "xfs: return errors from partial I/O failures to files" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xfs: return errors from partial I/O failures to files

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt28.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From ce5fa695122abeb62564438a40348a08bd9d4bf7 Mon Sep 17 00:00:00 2001
From: David Jeffery <djeffery at redhat.com>
Date: Fri, 28 Aug 2015 14:50:45 +1000
Subject: xfs: return errors from partial I/O failures to files

commit c9eb256eda4420c06bb10f5e8fbdbe1a34bc98e0 upstream.

There is an issue with xfs's error reporting in some cases of I/O partially
failing and partially succeeding. Calls like fsync() can report success even
though not all I/O was successful in partial-failure cases such as one disk of
a RAID0 array being offline.

The issue can occur when there are more than one bio per xfs_ioend struct.
Each call to xfs_end_bio() for a bio completing will write a value to
ioend->io_error.  If a successful bio completes after any failed bio, no
error is reported do to it writing 0 over the error code set by any failed bio.
The I/O error information is now lost and when the ioend is completed
only success is reported back up the filesystem stack.

xfs_end_bio() should only set ioend->io_error in the case of BIO_UPTODATE
being clear.  ioend->io_error is initialized to 0 at allocation so only needs
to be updated by a failed bio. Also check that ioend->io_error is 0 so that
the first error reported will be the error code returned.

Signed-off-by: David Jeffery <djeffery at redhat.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Signed-off-by: Dave Chinner <david at fromorbit.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/xfs/xfs_aops.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index e752236..ebc3107 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -377,7 +377,8 @@ xfs_end_bio(
 	xfs_ioend_t		*ioend = bio->bi_private;

 	ASSERT(atomic_read(&bio->bi_cnt) >= 1);
-	ioend->io_error = test_bit(BIO_UPTODATE, &bio->bi_flags) ? 0 : error;
+	if (!ioend->io_error && !test_bit(BIO_UPTODATE, &bio->bi_flags))
+		ioend->io_error = error;

 	/* Toss bio and pass work off to an xfsdatad thread */
 	bio->bi_private = NULL;
--
1.9.1