xfs: check reflink allocation mappings

There's a really bad bug in xfs_reflink_allocate_cow -- if bmapi_write
can return a zero error code but no mappings.  This happens if there's
an extent size hint (which causes allocation requests to be rounded to
extsz granularity internally), but there wasn't a big enough chunk of
free space to start filling at the extsz granularity and fill even one
block of the range that we actually requested.

In any case, if we got no mappings we can't possibly do anything useful
with the contents of imap, so we must bail out with ENOSPC here.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index c4f0aff86f96bec9fc9dfae6fe700b46e80d2bea..270246943a065fff8224b36b225e2572e213ef05 100644 (file)
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -464,6 +464,13 @@ retry:
        error = xfs_trans_commit(tp);
        if (error)
                return error;
+
+       /*
+        * Allocation succeeded but the requested range was not even partially
+        * satisfied?  Bail out!
+        */
+       if (nimaps == 0)
+               return -ENOSPC;
 convert:
        return xfs_reflink_convert_cow_extent(ip, imap, offset_fsb, count_fsb,
                        &dfops);