Patchwork jbd2: don't write superblock when unmounting an ro filesystem

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Submitter Eric Sandeen
Date July 24, 2012, 10:05 p.m.
Message ID <500F1C28.8010800@redhat.com>
Download mbox | patch
Permalink /patch/173055/
State Accepted, archived
Headers show

Comments

Eric Sandeen - July 24, 2012, 10:05 p.m.
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.

This behavior changed with:

commit 24bcc89c7e7c64982e6192b4952a0a92379fc341
Author: Jan Kara <jack@suse.cz>
Date:   Tue Mar 13 15:41:04 2012 -0400

    jbd2: split updating of journal superblock and marking journal empty

which lost some of the magic in jbd2_journal_update_superblock() which
used to test for a journal with no outstanding transactions.

I'm not sure if the following is quite the right approach, but it fixes
it for me.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

p.s. no idea why this only happens if I use a loop device with an offset!


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Eric Sandeen - July 24, 2012, 10:18 p.m.
On 7/24/12 5:05 PM, 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.
> 
> This behavior changed with:
> 
> commit 24bcc89c7e7c64982e6192b4952a0a92379fc341
> Author: Jan Kara <jack@suse.cz>
> Date:   Tue Mar 13 15:41:04 2012 -0400
> 
>     jbd2: split updating of journal superblock and marking journal empty
> 
> which lost some of the magic in jbd2_journal_update_superblock() which
> used to test for a journal with no outstanding transactions.
> 
> I'm not sure if the following is quite the right approach, but it fixes
> it for me.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> p.s. no idea why this only happens if I use a loop device with an offset!

PEBKAC.  no-offset ro loop mount does the same.

-Eric

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Lukas Czerner - July 26, 2012, 9:24 a.m.
On Tue, 24 Jul 2012, Eric Sandeen wrote:

> Date: Tue, 24 Jul 2012 17:05:28 -0500
> From: Eric Sandeen <sandeen@redhat.com>
> To: ext4 development <linux-ext4@vger.kernel.org>
> Cc: Jan Kara <jack@suse.cz>
> Subject: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem
> 
> 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

Hi Eric,

I am having hard time understanding what the sequence should be
doing. I actually can not reproduce it, because I can not create the
file system on such loop device because it seems like the size of
/dev/loop0 is zero, which makes sense considering that you set
offset to 65536 in the 65536 sized file.

Also, is the use of lo device really needed ? We can create the file
system on the file itself right ? Moreover, when I do that I can see
that the journal is not created because the device (file) is too
small, maybe it have something to do with the problem ?

Anyway, maybe I am missing something, but I do not understand what
kind of problem are you reproducing there.

-Lukas

> 
> 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.
> 
> This behavior changed with:
> 
> commit 24bcc89c7e7c64982e6192b4952a0a92379fc341
> Author: Jan Kara <jack@suse.cz>
> Date:   Tue Mar 13 15:41:04 2012 -0400
> 
>     jbd2: split updating of journal superblock and marking journal empty
> 
> which lost some of the magic in jbd2_journal_update_superblock() which
> used to test for a journal with no outstanding transactions.
> 
> I'm not sure if the following is quite the right approach, but it fixes
> it for me.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> p.s. no idea why this only happens if I use a loop device with an offset!
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index e9a3c4c..987ec76 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1354,6 +1354,11 @@ static void jbd2_mark_journal_empty(journal_t *journal)
>  
>  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
>  	read_lock(&journal->j_state_lock);
> +	/* Is it already empty? */
> +	if (sb->s_start == 0) {
> +		read_unlock(&journal->j_state_lock);
> +		return;
> +	}
>  	jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
>  		  journal->j_tail_sequence);
>  
> 
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Eric Sandeen - July 30, 2012, 3:49 p.m.
On 7/26/12 4:24 AM, Lukáš Czerner wrote:
> On Tue, 24 Jul 2012, Eric Sandeen wrote:
> 
>> Date: Tue, 24 Jul 2012 17:05:28 -0500
>> From: Eric Sandeen <sandeen@redhat.com>
>> To: ext4 development <linux-ext4@vger.kernel.org>
>> Cc: Jan Kara <jack@suse.cz>
>> Subject: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem
>>
>> 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
> 
> Hi Eric,
> 
> I am having hard time understanding what the sequence should be
> doing. I actually can not reproduce it, because I can not create the
> file system on such loop device because it seems like the size of
> /dev/loop0 is zero, which makes sense considering that you set
> offset to 65536 in the 65536 sized file.

sorry, that must have been a cut & paste error.  :(

The offset was leftover from trying to match the original reporter's case.  This simpler test shows the same problem:

 1014  truncate --size=2g fsfile
 1015  mkfs.ext4 fsfile
 1016  mount -o loop,ro fsfile mnt
 1017  umount mnt
 1018  dmesg | tail

[  417.631105] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
[  417.639183] SELinux: initialized (dev loop0, type ext4), uses xattr
[  420.903970] Buffer I/O error on device loop0, logical block 262144
[  420.910448] lost page write due to I/O error on loop0
[  420.915662] JBD2: Error -5 detected when updating journal superblock for loop0-8.

> Also, is the use of lo device really needed ? We can create the file
> system on the file itself right ? Moreover, when I do that I can see
> that the journal is not created because the device (file) is too
> small, maybe it have something to do with the problem ?
> 
> Anyway, maybe I am missing something, but I do not understand what
> kind of problem are you reproducing there.
> 
> -Lukas
> 
>>
>> 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.
>>
>> This behavior changed with:
>>
>> commit 24bcc89c7e7c64982e6192b4952a0a92379fc341
>> Author: Jan Kara <jack@suse.cz>
>> Date:   Tue Mar 13 15:41:04 2012 -0400
>>
>>     jbd2: split updating of journal superblock and marking journal empty
>>
>> which lost some of the magic in jbd2_journal_update_superblock() which
>> used to test for a journal with no outstanding transactions.
>>
>> I'm not sure if the following is quite the right approach, but it fixes
>> it for me.
>>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> ---
>>
>> p.s. no idea why this only happens if I use a loop device with an offset!
>>
>> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
>> index e9a3c4c..987ec76 100644
>> --- a/fs/jbd2/journal.c
>> +++ b/fs/jbd2/journal.c
>> @@ -1354,6 +1354,11 @@ static void jbd2_mark_journal_empty(journal_t *journal)
>>  
>>  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
>>  	read_lock(&journal->j_state_lock);
>> +	/* Is it already empty? */
>> +	if (sb->s_start == 0) {
>> +		read_unlock(&journal->j_state_lock);
>> +		return;
>> +	}
>>  	jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
>>  		  journal->j_tail_sequence);
>>  
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>

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Jan Kara - Aug. 15, 2012, 12:14 p.m.
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

> This behavior changed with:
> 
> commit 24bcc89c7e7c64982e6192b4952a0a92379fc341
> Author: Jan Kara <jack@suse.cz>
> Date:   Tue Mar 13 15:41:04 2012 -0400
> 
>     jbd2: split updating of journal superblock and marking journal empty
> 
> which lost some of the magic in jbd2_journal_update_superblock() which
> used to test for a journal with no outstanding transactions.
> 
> I'm not sure if the following is quite the right approach, but it fixes
> it for me.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> p.s. no idea why this only happens if I use a loop device with an offset!
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index e9a3c4c..987ec76 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1354,6 +1354,11 @@ static void jbd2_mark_journal_empty(journal_t *journal)
>  
>  	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
>  	read_lock(&journal->j_state_lock);
> +	/* Is it already empty? */
> +	if (sb->s_start == 0) {
> +		read_unlock(&journal->j_state_lock);
> +		return;
> +	}
>  	jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
>  		  journal->j_tail_sequence);
>  
>
Eric Sandeen - Aug. 15, 2012, 5:25 p.m.
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
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Theodore Ts'o - Aug. 18, 2012, 6:45 p.m.
Applied, thanks.  I updated the reproduction instructions so that they
wored correctly.  (i.e., by removing the offset, and changing the size
to 1g).

					- Ted
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Eric Sandeen - Aug. 19, 2012, 6:54 p.m.
On Aug 18, 2012, at 11:45 AM, "Theodore Ts'o" <tytso@mit.edu> wrote:

> Applied, thanks.  I updated the reproduction instructions so that they
> wored correctly.  (i.e., by removing the offset, and changing the size
> to 1g).
> 
Thanks, sorry about that really messed up commit message.  :(

-Eric

>                    - Ted
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Patch

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index e9a3c4c..987ec76 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1354,6 +1354,11 @@  static void jbd2_mark_journal_empty(journal_t *journal)
 
 	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
 	read_lock(&journal->j_state_lock);
+	/* Is it already empty? */
+	if (sb->s_start == 0) {
+		read_unlock(&journal->j_state_lock);
+		return;
+	}
 	jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
 		  journal->j_tail_sequence);