xfs: fix potential infinite loop in xfs_iomap_prealloc_size()

If freesp == 0, we could end up in an infinite loop while squashing
the preallocation. Break the loop when we've killed the prealloc
entirely.

Signed-off-by: Brian Foster <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Signed-off-by: Ben Myers <[email protected]>
(cherry picked from commit e78c420bfc2608bb5f9a0b9165b1071c1e31166a)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 912d83d8860a984a938b604f3e2447c3e390ce89..b0b0f448e8434a08ccaf6fc4f75b9b23a2ad6c51 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -413,7 +413,7 @@ xfs_iomap_prealloc_size(
                 * have a large file on a small filesystem and the above
                 * lowspace thresholds are smaller than MAXEXTLEN.
                 */
-               while (alloc_blocks >= freesp)
+               while (alloc_blocks && alloc_blocks >= freesp)
                        alloc_blocks >>= 4;
        }