[ 3.8.y.z extended stable ] Patch "ext4: limit group search loop for non-extent files" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ext4: limit group search loop for non-extent files

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d2ce65ddc7d24b19f0184382857ec2a0c9c44085 Mon Sep 17 00:00:00 2001
From: Lachlan McIlroy <lmcilroy at redhat.com>
Date: Sun, 5 May 2013 23:10:00 -0400
Subject: ext4: limit group search loop for non-extent files

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