linux-kernel - [ 06/49] ext4: do not try to write superblock on ro remount w/o journal

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Message-Id: <20130113174257.120720127@decadent.org.uk>
Date:	Sun, 13 Jan 2013 17:43:01 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Michael Tokarev <mjt@....msk.ru>,
	"Theodore Tso" <tytso@....edu>
Subject: [ 06/49] ext4: do not try to write superblock on ro remount w/o journal

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

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

From: Michael Tokarev <mjt@....msk.ru>

commit d096ad0f79a782935d2e06ae8fb235e8c5397775 upstream.

When a journal-less ext4 filesystem is mounted on a read-only block
device (blockdev --setro will do), each remount (for other, unrelated,
flags, like suid=>nosuid etc) results in a series of scary messages
from kernel telling about I/O errors on the device.

This is becauese of the following code ext4_remount():

       if (sbi->s_journal == NULL)
                ext4_commit_super(sb, 1);

at the end of remount procedure, which forces writing (flushing) of
a superblock regardless whenever it is dirty or not, if the filesystem
is readonly or not, and whenever the device itself is readonly or not.

We only need call ext4_commit_super when the file system had been
previously mounted read/write.

Thanks to Eric Sandeen for help in diagnosing this issue.

Signed-off-By: Michael Tokarev <mjt@....msk.ru>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4969167..183ae34 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4729,7 +4729,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 	}

 	ext4_setup_system_zone(sb);
-	if (sbi->s_journal == NULL)
+	if (sbi->s_journal == NULL && !(old_sb_flags & MS_RDONLY))
 		ext4_commit_super(sb, 1);

 #ifdef CONFIG_QUOTA

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