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>

diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index 077c341..d438132 100644 (file)
--- 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;
 }