[PATCH v2] xfs: return errors from partial I/O failures to files

[David Jeffery <djeffery@xxxxxxxxxx>]

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

---

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 3859f5e..458fced 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -356,7 +356,8 @@ xfs_end_bio(
 {
        xfs_ioend_t             *ioend = bio->bi_private;
 
-       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;