xfs: ensure we capture IO errors correctly

Failed buffer readahead can leave the buffer in the cache marked
with an error. Most callers that then issue a subsequent read on the
buffer do not zero the b_error field out, and so we may incorectly
detect an error during IO completion due to the stale error value
left on the buffer.

Avoid this problem by zeroing the error before IO submission. This
ensures that the only IO errors that are detected those captured
from are those captured from bio submission or completion.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
(cherry picked from commit c163f9a1760229a95d04e37b332de7d5c1c225cd)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 4e8f0df82d025e6bc38615a94d254bf003c24972..8459b5d8cb71ceaa98ff64990cae8d4daaf6f1b1 100644 (file)
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1334,6 +1334,12 @@ _xfs_buf_ioapply(
        int             size;
        int             i;
 
+       /*
+        * Make sure we capture only current IO errors rather than stale errors
+        * left over from previous use of the buffer (e.g. failed readahead).
+        */
+       bp->b_error = 0;
+
        if (bp->b_flags & XBF_WRITE) {
                if (bp->b_flags & XBF_SYNCIO)
                        rw = WRITE_SYNC;