potential memory leak on transaction commit

potential memory leak on transaction commit

[Zhang Huan]

Hi all,

There is potential memory leak of journal head in function
jbd2_journal_commit_transaction. The problem is that JBD2 will not
reclaim the journal head of commit record if error occurs or journal is
abotred.

I use the following script to reproduce this issue, on a RHEL6 system. I
found it very easy to reproduce with async commit enabled.

mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
touch /mnt/xxx
echo offline > /sys/block/sdb/device/state
sync
umount /mnt
rmmod ext4
rmmod jbd2

Removal of the jbd2 module will make slab complaining that
"cache `jbd2_journal_head': can't free all objects".


Here is my fix for this issue. The commit record should be reclaimed no
matter error occurs or not.

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index f3ad159..37a973a 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t *journal,
 	int ret;
 	struct timespec now = current_kernel_time();
 
+	*cbh = NULL;
+
 	if (is_journal_aborted(journal))
 		return 0;
 
@@ -808,7 +810,7 @@ wait_for_iobuf:
 		if (err)
 			__jbd2_journal_abort_hard(journal);
 	}
-	if (!err && !is_journal_aborted(journal))
+	if (cbh)
 		err = journal_wait_on_commit_record(journal, cbh);
 	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
 				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&



PS: Just out of curiosity, why would journal_submit_commit_record return a
value of 1 instead of an error number if get descriptor buffer is failed.


Zhang Huan

Re: potential memory leak on transaction commit

[Lukas Czerner]

On Tue, 8 Mar 2011, Zhang Huan wrote:

> Hi all,
> 
> There is potential memory leak of journal head in function
> jbd2_journal_commit_transaction. The problem is that JBD2 will not
> reclaim the journal head of commit record if error occurs or journal is
> abotred.
> 
> I use the following script to reproduce this issue, on a RHEL6 system. I
> found it very easy to reproduce with async commit enabled.
> 
> mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
> touch /mnt/xxx
> echo offline > /sys/block/sdb/device/state
> sync
> umount /mnt
> rmmod ext4
> rmmod jbd2
> 
> Removal of the jbd2 module will make slab complaining that
> "cache `jbd2_journal_head': can't free all objects".
> 
> 
> Here is my fix for this issue. The commit record should be reclaimed no
> matter error occurs or not.
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index f3ad159..37a973a 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t *journal,
>  	int ret;
>  	struct timespec now = current_kernel_time();
>  
> +	*cbh = NULL;
> +
>  	if (is_journal_aborted(journal))
>  		return 0;
>  
> @@ -808,7 +810,7 @@ wait_for_iobuf:
>  		if (err)
>  			__jbd2_journal_abort_hard(journal);
>  	}
> -	if (!err && !is_journal_aborted(journal))
> +	if (cbh)

Hi,

I wonder if we could do rather this:

	if (!err && !is_journal_aborted(journal))
		err = journal_wait_on_commit_record(journal, cbh);
	else if (cbh) {
		put_bh(cbh);
		jbd2_journal_put_journal_head(bh2jh(cbh));
	}

I think this is more readable...

Thanks!
-Lukas

>  		err = journal_wait_on_commit_record(journal, cbh);
>  	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
>  				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
> 
> 
> 
> PS: Just out of curiosity, why would journal_submit_commit_record return a
> value of 1 instead of an error number if get descriptor buffer is failed.
> 
> 
> Zhang Huan
> --
> 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
> 

-- 

Re: potential memory leak on transaction commit

[Zhang Huan]

On Tue, 8 Mar 2011, Lukas Czerner wrote:

> On Tue, 8 Mar 2011, Zhang Huan wrote:
>
>> Hi all,
>>
>> There is potential memory leak of journal head in function
>> jbd2_journal_commit_transaction. The problem is that JBD2 will not
>> reclaim the journal head of commit record if error occurs or journal is
>> abotred.
>>
>> I use the following script to reproduce this issue, on a RHEL6 system. I
>> found it very easy to reproduce with async commit enabled.
>>
>> mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
>> touch /mnt/xxx
>> echo offline > /sys/block/sdb/device/state
>> sync
>> umount /mnt
>> rmmod ext4
>> rmmod jbd2
>>
>> Removal of the jbd2 module will make slab complaining that
>> "cache `jbd2_journal_head': can't free all objects".
>>
>>
>> Here is my fix for this issue. The commit record should be reclaimed no
>> matter error occurs or not.
>>
>> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
>> index f3ad159..37a973a 100644
>> --- a/fs/jbd2/commit.c
>> +++ b/fs/jbd2/commit.c
>> @@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t *journal,
>>  	int ret;
>>  	struct timespec now = current_kernel_time();
>>
>> +	*cbh = NULL;
>> +
>>  	if (is_journal_aborted(journal))
>>  		return 0;
>>
>> @@ -808,7 +810,7 @@ wait_for_iobuf:
>>  		if (err)
>>  			__jbd2_journal_abort_hard(journal);
>>  	}
>> -	if (!err && !is_journal_aborted(journal))
>> +	if (cbh)
>
> Hi,
>
> I wonder if we could do rather this:
>
> 	if (!err && !is_journal_aborted(journal))
> 		err = journal_wait_on_commit_record(journal, cbh);
> 	else if (cbh) {
> 		put_bh(cbh);
> 		jbd2_journal_put_journal_head(bh2jh(cbh));
> 	}
>
> I think this is more readable...

Hi,

I don't think it is a good idea. Anyway, you need to wait for buffer to 
complete, and then release journal head on it. That is exactly what 
journal_wait_on_commit_record does.

>
> Thanks!
> -Lukas
>
>>  		err = journal_wait_on_commit_record(journal, cbh);
>>  	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
>>  				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
>>
>>
>>
>> PS: Just out of curiosity, why would journal_submit_commit_record return a
>> value of 1 instead of an error number if get descriptor buffer is failed.
>>
>>
>> Zhang Huan
>> --
>> 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
>>
>
> -- 
>

Zhang Huan

Re: potential memory leak on transaction commit

[Lukas Czerner]

On Tue, 8 Mar 2011, Zhang Huan wrote:

> 
> On Tue, 8 Mar 2011, Lukas Czerner wrote:
> 
> > On Tue, 8 Mar 2011, Zhang Huan wrote:
> > 
> > > Hi all,
> > > 
> > > There is potential memory leak of journal head in function
> > > jbd2_journal_commit_transaction. The problem is that JBD2 will not
> > > reclaim the journal head of commit record if error occurs or journal is
> > > abotred.
> > > 
> > > I use the following script to reproduce this issue, on a RHEL6 system. I
> > > found it very easy to reproduce with async commit enabled.
> > > 
> > > mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
> > > touch /mnt/xxx
> > > echo offline > /sys/block/sdb/device/state
> > > sync
> > > umount /mnt
> > > rmmod ext4
> > > rmmod jbd2
> > > 
> > > Removal of the jbd2 module will make slab complaining that
> > > "cache `jbd2_journal_head': can't free all objects".
> > > 
> > > 
> > > Here is my fix for this issue. The commit record should be reclaimed no
> > > matter error occurs or not.
> > > 
> > > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> > > index f3ad159..37a973a 100644
> > > --- a/fs/jbd2/commit.c
> > > +++ b/fs/jbd2/commit.c
> > > @@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t
> > > *journal,
> > >  	int ret;
> > >  	struct timespec now = current_kernel_time();
> > > 
> > > +	*cbh = NULL;
> > > +
> > >  	if (is_journal_aborted(journal))
> > >  		return 0;
> > > 
> > > @@ -808,7 +810,7 @@ wait_for_iobuf:
> > >  		if (err)
> > >  			__jbd2_journal_abort_hard(journal);
> > >  	}
> > > -	if (!err && !is_journal_aborted(journal))
> > > +	if (cbh)
> > 
> > Hi,
> > 
> > I wonder if we could do rather this:
> > 
> > 	if (!err && !is_journal_aborted(journal))
> > 		err = journal_wait_on_commit_record(journal, cbh);
> > 	else if (cbh) {
> > 		put_bh(cbh);
> > 		jbd2_journal_put_journal_head(bh2jh(cbh));
> > 	}
> > 
> > I think this is more readable...
> 
> Hi,
> 
> I don't think it is a good idea. Anyway, you need to wait for buffer to
> complete, and then release journal head on it. That is exactly what
> journal_wait_on_commit_record does.

Oh, I see. Ok then ignore me :)

Thanks!
-Lukas

> 
> > 
> > Thanks!
> > -Lukas
> > 
> > >  		err = journal_wait_on_commit_record(journal, cbh);
> > >  	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
> > >  				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
> > > 
> > > 
> > > 
> > > PS: Just out of curiosity, why would journal_submit_commit_record return a
> > > value of 1 instead of an error number if get descriptor buffer is failed.
> > > 
> > > 
> > > Zhang Huan
> > > --
> > > 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
> > > 
> > 
> > -- 
> > 
> 
> Zhang Huan
> 

-- 

Re: potential memory leak on transaction commit

[Zhang Huan]

Hi,

I would like to know if there is more comment on this?

On Tue, Mar 8, 2011 at 19:40, Zhang Huan <zhhuan@gmail.com> wrote:
> Hi all,
>
> There is potential memory leak of journal head in function
> jbd2_journal_commit_transaction. The problem is that JBD2 will not
> reclaim the journal head of commit record if error occurs or journal is
> abotred.
>
> I use the following script to reproduce this issue, on a RHEL6 system. I
> found it very easy to reproduce with async commit enabled.
>
> mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
> touch /mnt/xxx
> echo offline > /sys/block/sdb/device/state
> sync
> umount /mnt
> rmmod ext4
> rmmod jbd2
>
> Removal of the jbd2 module will make slab complaining that
> "cache `jbd2_journal_head': can't free all objects".
>
>
> Here is my fix for this issue. The commit record should be reclaimed no
> matter error occurs or not.
>
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index f3ad159..37a973a 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t *journal,
>        int ret;
>        struct timespec now = current_kernel_time();
>
> +       *cbh = NULL;
> +
>        if (is_journal_aborted(journal))
>                return 0;
>
> @@ -808,7 +810,7 @@ wait_for_iobuf:
>                if (err)
>                        __jbd2_journal_abort_hard(journal);
>        }
> -       if (!err && !is_journal_aborted(journal))
> +       if (cbh)
>                err = journal_wait_on_commit_record(journal, cbh);
>        if (JBD2_HAS_INCOMPAT_FEATURE(journal,
>                                      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
>
>
>
> PS: Just out of curiosity, why would journal_submit_commit_record return a
> value of 1 instead of an error number if get descriptor buffer is failed.
>
>
> Zhang Huan
>

Zhang Huan
--
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Re: potential memory leak on transaction commit

[Ted Ts'o]

Hi Zhang,

Sorry for the delay in looking at it.  One thing which is missing from
your patch is a signed-off-by header.  From section 12 of the
Documentation/SubmittingPatches file in the Linux source tree:

>The sign-off is a simple line at the end of the explanation for the
>patch, which certifies that you wrote it or otherwise have the right to
>pass it on as a open-source patch.  The rules are pretty simple: if you
>can certify the below:
>
>        Developer's Certificate of Origin 1.1
>
>        By making a contribution to this project, I certify that:
>
>        (a) The contribution was created in whole or in part by me and I
>            have the right to submit it under the open source license
>            indicated in the file; or
>
>        (b) The contribution is based upon previous work that, to the best
>            of my knowledge, is covered under an appropriate open source
>            license and I have the right under that license to submit that
>            work with modifications, whether created in whole or in part
>            by me, under the same open source license (unless I am
>            permitted to submit under a different license), as indicated
>            in the file; or
>
>        (c) The contribution was provided directly to me by some other
>            person who certified (a), (b) or (c) and I have not modified
>            it.
>
>	(d) I understand and agree that this project and the contribution
>	    are public and that a record of the contribution (including all
>	    personal information I submit with it, including my sign-off) is
>	    maintained indefinitely and may be redistributed consistent with
>	    this project or the open source license(s) involved.
>
>then you just add a line saying
>
>	Signed-off-by: Random J Developer <random@developer.example.org>
>
>using your real name (sorry, no pseudonyms or anonymous contributions.)

If you could send me an acknowledgement that it would be OK to add a

Signed-off-by: Zhang Huan <zhhuan@gmail.com>

line to your patch, it would be much appreciated.

     	     	       	     	     - Ted

Re: potential memory leak on transaction commit

[Zhang Huan]

On Tue, Apr 5, 2011 at 06:10, Ted Ts'o <tytso@mit.edu> wrote:
>
> If you could send me an acknowledgement that it would be OK to add a
>
> Signed-off-by: Zhang Huan <zhhuan@gmail.com>
>
> line to your patch, it would be much appreciated.
>

Yes. please go ahead.

Zhang Huan

Re: potential memory leak on transaction commit

[Ted Ts'o]

On Tue, Apr 05, 2011 at 08:35:35PM +0800, Zhang Huan wrote:
> On Tue, Apr 5, 2011 at 06:10, Ted Ts'o <tytso@mit.edu> wrote:
> >
> > If you could send me an acknowledgement that it would be OK to add a
> >
> > Signed-off-by: Zhang Huan <zhhuan@gmail.com>
> >
> > line to your patch, it would be much appreciated.
> >
> 
> Yes. please go ahead.

Thanks, I've added your patch to the ext4 patch queue.

	     	   	      	     - Ted