xfs: Fix rounding in xfs_alloc_fix_len()

Rounding in xfs_alloc_fix_len() is wrong. As the comment states, the
result should be a number of a form (k*prod+mod) however due to sign
mistake the result is different. As a result allocations on raid arrays
could be misaligned in some cases.

This also seems to fix occasional assertion failure:
	XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0)
in xfs_alloc_ag_vextent_size().

Also add an assertion that the result of xfs_alloc_fix_len() is of
expected form.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 8 insertions, 10 deletions

diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index 077c3417a54e..d43813267a80 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -257,16 +257,14 @@ xfs_alloc_fix_len(
         k = rlen % args->prod;
         if (k == args->mod)
                 return;
-        if (k > args->mod) {
-                if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
-                        return;
-        } else {
-                if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
-                    (int)args->minlen)
-                        return;
-        }
-        ASSERT(rlen >= args->minlen);
-        ASSERT(rlen <= args->maxlen);
+        if (k > args->mod)
+                rlen = rlen - (k - args->mod);
+        else
+                rlen = rlen - args->prod + (args->mod - k);
+        if ((int)rlen < (int)args->minlen)
+                return;
+        ASSERT(rlen >= args->minlen && rlen <= args->maxlen);
+        ASSERT(rlen % args->prod == args->mod);
         args->len = rlen;
 }