[3.13.y.z extended stable] Patch "ext4: fix ext4_discard_allocated_blocks() if we can't allocate the pa struct" 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: fix ext4_discard_allocated_blocks() if we can't allocate the pa struct

to the linux-3.13.y-queue branch of the 3.13.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-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.7.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 2b6fd2c3521311fbf7ba18ee17141e6b102f29cb Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Wed, 30 Jul 2014 22:17:17 -0400
Subject: ext4: fix ext4_discard_allocated_blocks() if we can't allocate the pa
 struct

commit 86f0afd463215fc3e58020493482faa4ac3a4d69 upstream.

If there is a failure while allocating the preallocation structure, a
number of blocks can end up getting marked in the in-memory buddy
bitmap, and then not getting released.  This can result in the
following corruption getting reported by the kernel:

EXT4-fs error (device sda3): ext4_mb_generate_buddy:758: group 1126,
12793 clusters in bitmap, 12729 in gd

In that case, we need to release the blocks using mb_free_blocks().

Tested: fs smoke test; also demonstrated that with injected errors,
	the file system is no longer getting corrupted

Google-Bug-Id: 16657874

Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ext4/mballoc.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 502f0fd..795d5af 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3196,8 +3196,27 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
 static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
 {
 	struct ext4_prealloc_space *pa = ac->ac_pa;
+	struct ext4_buddy e4b;
+	int err;

-	if (pa && pa->pa_type == MB_INODE_PA)
+	if (pa == NULL) {
+		err = ext4_mb_load_buddy(ac->ac_sb, ac->ac_f_ex.fe_group, &e4b);
+		if (err) {
+			/*
+			 * This should never happen since we pin the
+			 * pages in the ext4_allocation_context so
+			 * ext4_mb_load_buddy() should never fail.
+			 */
+			WARN(1, "mb_load_buddy failed (%d)", err);
+			return;
+		}
+		ext4_lock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
+		mb_free_blocks(ac->ac_inode, &e4b, ac->ac_f_ex.fe_start,
+			       ac->ac_f_ex.fe_len);
+		ext4_unlock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
+		return;
+	}
+	if (pa->pa_type == MB_INODE_PA)
 		pa->pa_free += ac->ac_b_ex.fe_len;
 }

--
1.9.1