[3.13.y.z extended stable] Patch "ext4: check s_chksum_driver when looking for bg csum presence" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Fri Oct 31 20:53:38 UTC 2014

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

    ext4: check s_chksum_driver when looking for bg csum presence

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

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



>From cd41334c2b76bc575e2772a539ca20c7fa7f29e6 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong at oracle.com>
Date: Tue, 14 Oct 2014 02:35:49 -0400
Subject: ext4: check s_chksum_driver when looking for bg csum presence

commit 813d32f91333e4c33d5a19b67167c4bae42dae75 upstream.

Convert the ext4_has_group_desc_csum predicate to look for a checksum
driver instead of the metadata_csum flag and change the bg checksum
calculation function to look for GDT_CSUM before taking the crc16

Without this patch, if we mount with ^uninit_bg,^metadata_csum and
later metadata_csum gets turned on by accident, the block group
checksum functions will incorrectly assume that checksumming is
enabled (metadata_csum) but that crc16 should be used
(!s_chksum_driver).  This is totally wrong, so fix the predicate
and the checksum formula selection.

(Granted, if the metadata_csum feature bit gets enabled on a live FS
then something underhanded is going on, but we could at least avoid
writing garbage into the on-disk fields.)

Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Reviewed-by: Dmitry Monakhov <dmonakhov at openvz.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 fs/ext4/ext4.h  | 4 ++--
 fs/ext4/super.c | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5b250fe..bfb7fed 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2337,8 +2337,8 @@ extern int ext4_register_li_request(struct super_block *sb,
 static inline int ext4_has_group_desc_csum(struct super_block *sb)
+	       (EXT4_SB(sb)->s_chksum_driver != NULL);

 static inline int ext4_has_metadata_csum(struct super_block *sb)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6686ce4..608db58 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2019,6 +2019,10 @@ static __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,

 	/* old crc16 code */
+	if (!(sbi->s_es->s_feature_ro_compat &
+	      cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)))
+		return 0;
 	offset = offsetof(struct ext4_group_desc, bg_checksum);

 	crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));

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