[PATCH 15/78] ext4: limit group search loop for non-extent files

[Kamal Mostafa]

3.8.13.1 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lachlan McIlroy <lmcilroy at redhat.com>

commit e6155736ad76b2070652745f9e54cdea3f0d8567 upstream.

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 at redhat.com: add commit msg & comments]

Signed-off-by: Lachlan McIlroy <lmcilroy at redhat.com>
Signed-off-by: Eric Sandeen <sandeen at redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ext4/mballoc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index b443e62..1206682 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1983,7 +1983,11 @@ 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 */
-- 
1.8.1.2