xfs: xfs_trans_read_buf() should return an error on failure

When inside a transaction and we fail to read a buffer,
xfs_trans_read_buf returns a null buffer pointer and no error.
xfs_do_da_buf() checks the error return, but not the buffer, and as
a result this read failure condition causes a panic when it attempts
to dereference the non-existant buffer.

Make xfs_trans_read_buf() return the same error for this situation
regardless of whether it is in a transaction or not. This means
every caller does not need to check both the error return and the
buffer before proceeding to use the buffer.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
index 3bea66132334..03b3b7f85a3b 100644
--- a/fs/xfs/xfs_trans_buf.c
+++ b/fs/xfs/xfs_trans_buf.c
@@ -383,7 +383,8 @@ xfs_trans_read_buf(
         bp = xfs_buf_read(target, blkno, len, flags | XBF_DONT_BLOCK);
         if (bp == NULL) {
                 *bpp = NULL;
-                return 0;
+                return (flags & XBF_TRYLOCK) ?
+                                        0 : XFS_ERROR(ENOMEM);
         }
         if (XFS_BUF_GETERROR(bp) != 0) {
             XFS_BUF_SUPER_STALE(bp);