ext4: limit group search loop for non-extent files

In the case where we are allocating for a non-extent file,
we must limit the groups we allocate from to those below
2^32 blocks, and ext4_mb_regular_allocator() attempts to
do this initially by putting a cap on ngroups for the
subsequent search loop.

However, the initial target group comes in from the
allocation context (ac), and it may already be beyond
the artificially limited ngroups.  In this case,
the limit

	if (group == ngroups)
		group = 0;

at the top of the loop is never true, and the loop will
run away.

Catch this case inside the loop and reset the search to
start at group 0.

[sandeen@redhat.com: add commit msg & comments]

Signed-off-by: Lachlan McIlroy <lmcilroy@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a11ea4d6164c2593411517473d6543160cec1f6e..39d30f12d98de24157ab202b7240b5813b2f3907 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2105,7 +2105,11 @@ repeat:
                group = ac->ac_g_ex.fe_group;
 
                for (i = 0; i < ngroups; group++, i++) {
-                       if (group == ngroups)
+                       /*
+                        * Artificially restricted ngroups for non-extent
+                        * files makes group > ngroups possible on first loop.
+                        */
+                       if (group >= ngroups)
                                group = 0;
 
                        /* This now checks without needing the buddy page */