Re: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem

[Eric Sandeen <esandeen@redhat.com>]

On 8/15/12 7:14 AM, Jan Kara wrote:
> On Tue 24-07-12 17:05:28, Eric Sandeen wrote:
>> This sequence:
>>
>> # truncate --size=65536 fsfile
>> # losetup --offset 65536 /dev/loop0 fsfile
>> # mkfs.ext4 /dev/loop0
>> # losetup -d /dev/loop0
>> # mount -o loop,ro,offset=65536 fsfile  mnt/
>> # umount mnt
>> # dmesg | tail
>>
>> results in an IO error when unmounting the RO filesystem:
>>
>> [  312.386074] SELinux: initialized (dev loop1, type ext4), uses xattr
>> [  318.020828] Buffer I/O error on device loop1, logical block 196608
>> [  318.027024] lost page write due to I/O error on loop1
>> [  318.032088] JBD2: Error -5 detected when updating journal superblock for loop1-8.
>    Ted, did this patch fall through cracks? I've ported the fix to JBD and
> added it to my tree. I plan to send it to Linus in a few days. Also I've
> CC'd stable since this is a bit annoying regression.
>
> 								Honza


Thanks for doing both of those things, Jan.

BTW this happens on loop because mount -o,ro apparently sets up the loop 
device itself as readonly.

-Eric