Re: Re: Re: EXT4 regression caused 4eec7

Re: Re: Re: EXT4 regression caused 4eec7

[EUNBONG SONG]

>> Since at this point it's safer to rollback the change and we can
>> investigate more deeply how to fix it correctly for the next
>> development cycle, this is the patch which I'm testing.

>>                     - Ted

> Hello, I've tested with your patch. But the same problem was reproduced.
> Currently, I'm trying to git bisect. If i done git bisect, i will let you know.

Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
I don't know the root cause. 


Signed-off-by: Eunbong Song <eunb.song@samsung.com>
---
 include/linux/journal-head.h |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/journal-head.h b/include/linux/journal-head.h
index 13a3da2..c18b46f 100644
--- a/include/linux/journal-head.h
+++ b/include/linux/journal-head.h
@@ -31,14 +31,21 @@ struct journal_head {
 	/*
 	 * Journalling list for this buffer [jbd_lock_bh_state()]
 	 */
-	unsigned b_jlist:4;
+	unsigned b_jlist;
 
 	/*
 	 * This flag signals the buffer has been modified by
 	 * the currently running transaction
 	 * [jbd_lock_bh_state()]
 	 */
-	unsigned b_modified:1;
+	unsigned b_modified;
+
+	/*
+	 * This feild tracks the last transaction id in which this buffer
+	 * has been cowed
+	 * [jbd_lock_bh_state()]
+	 */
+	tid_t b_cow_tid;
 
 	/*
 	 * Copy of the buffer data frozen for writing to the log.
-- 
1.7.0.4


Thanks. 

Re: Re: Re: EXT4 regression caused 4eec7

[Dmitry Monakhov]

On Sun, 12 May 2013 13:05:00 +0000 (GMT), EUNBONG SONG <eunb.song@samsung.com> wrote:
> 
> 
> >> Since at this point it's safer to rollback the change and we can
> >> investigate more deeply how to fix it correctly for the next
> >> development cycle, this is the patch which I'm testing.
> 
> >>                     - Ted
> 
> > Hello, I've tested with your patch. But the same problem was reproduced.
> > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> 
> Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
OK that explains both regressions ext4/jbd2 and ext3/jbd(https://lkml.org/lkml/2013/5/10/434)
Probably some race because b_jlist accessed w/o lock some places. 
BUT i still can not reproduce original issue :(
I've tried all types of disks near me (ssd,hdd,usb-dongle),
What disk type you use? Is it reproducible on x86?
Please post following info:
#fdisk -l  $HDD
#hdparm -t $HDD
#df -h 
#cat /proc/mounts

> I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> I don't know the root cause. 
> 
> 
> Signed-off-by: Eunbong Song <eunb.song@samsung.com>
> ---
>  include/linux/journal-head.h |   11 +++++++++--
>  1 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/journal-head.h b/include/linux/journal-head.h
> index 13a3da2..c18b46f 100644
> --- a/include/linux/journal-head.h
> +++ b/include/linux/journal-head.h
> @@ -31,14 +31,21 @@ struct journal_head {
>  	/*
>  	 * Journalling list for this buffer [jbd_lock_bh_state()]
>  	 */
> -	unsigned b_jlist:4;
> +	unsigned b_jlist;
>  
>  	/*
>  	 * This flag signals the buffer has been modified by
>  	 * the currently running transaction
>  	 * [jbd_lock_bh_state()]
>  	 */
> -	unsigned b_modified:1;
> +	unsigned b_modified;
> +
> +	/*
> +	 * This feild tracks the last transaction id in which this buffer
> +	 * has been cowed
> +	 * [jbd_lock_bh_state()]
> +	 */
> +	tid_t b_cow_tid;
>  
>  	/*
>  	 * Copy of the buffer data frozen for writing to the log.
> -- 
> 1.7.0.4
> 
> 
> Thanks. N‹㎠咽r›y鉉šbXФ푤v^–)頻{.n+‰램Š{‘喩zX㎍›●}ž꼿z&j:+v‰㉭\a‘喩zZ+€+zf＂hšˆ~††i鎬zwⅱ?™②&)刪f”^j푹ym…@Aa뛴\x7f\f0띠h’i\x7f

Re: Re: Re: EXT4 regression caused 4eec7

[Jan Kara]

On Sun 12-05-13 13:04:59, EUNBONG SONG wrote:
> 
> 
> >> Since at this point it's safer to rollback the change and we can
> >> investigate more deeply how to fix it correctly for the next
> >> development cycle, this is the patch which I'm testing.
> 
> >>                     - Ted
> 
> > Hello, I've tested with your patch. But the same problem was reproduced.
> > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> 
> Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
> I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> I don't know the root cause. 
  This is really strange. I've verified the code and all the places
modifying b_jlist or b_modified are holding bh_state lock so we should be
safe...

Hum, but I remember I was debugging similar problems with bit fields in
btrfs on ia64 as well (see http://lwn.net/Articles/478657/). So I think what
has happened is that your compiler compiled bitfield access as 64-bit and
updates to b_jcount and b_jlist / b_modified crashed into one another. I
didn't hit it because my compiler was not so "clever".

Grumble. In this case I think bitfields are not worth the trouble with gcc.
It's a pitty we have to spend additional 8 bytes for every journal_head but
we'll survive... I'll send Ted a partial revert and add a comment so that
we won't repeat this mistake in future.

								Honza
 
> Signed-off-by: Eunbong Song <eunb.song@samsung.com>
> ---
>  include/linux/journal-head.h |   11 +++++++++--
>  1 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/journal-head.h b/include/linux/journal-head.h
> index 13a3da2..c18b46f 100644
> --- a/include/linux/journal-head.h
> +++ b/include/linux/journal-head.h
> @@ -31,14 +31,21 @@ struct journal_head {
>  	/*
>  	 * Journalling list for this buffer [jbd_lock_bh_state()]
>  	 */
> -	unsigned b_jlist:4;
> +	unsigned b_jlist;
>  
>  	/*
>  	 * This flag signals the buffer has been modified by
>  	 * the currently running transaction
>  	 * [jbd_lock_bh_state()]
>  	 */
> -	unsigned b_modified:1;
> +	unsigned b_modified;
> +
> +	/*
> +	 * This feild tracks the last transaction id in which this buffer
> +	 * has been cowed
> +	 * [jbd_lock_bh_state()]
> +	 */
> +	tid_t b_cow_tid;
>  
>  	/*
>  	 * Copy of the buffer data frozen for writing to the log.
> -- 
> 1.7.0.4
> 
> 
> Thanks. 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: EXT4 regression caused 4eec7

[Theodore Ts'o]

On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> Grumble. In this case I think bitfields are not worth the trouble with gcc.
> It's a pitty we have to spend additional 8 bytes for every journal_head but
> we'll survive... I'll send Ted a partial revert and add a comment so that
> we won't repeat this mistake in future.

Or just switch things to use explicit 32-bit boolean operations.
Sounds the safest way to go is to simply not trust bitfields to be
something gcc is competent to compile correctly, and just open code it
in standard C.  (Large portions of ext4 and e2fsprogs do this
manually, for historical reasons, and it sounds like we have a good
reason to do it going forward.)

Jan, Dmitry --- I still have in my tree a revert for commit 4eec708d2:
ext4: use io_end for multiple bios, since I belive Dmitry still
bisected a regression for xfstests 299.  Dmitry, can you confirm that
you are definitely seeing a regression here?  Jan, do you mind if we
try to figure out how to fix this during the next development cycle,
since it was part of your much longer, extensive patch series anyway?

I've determined that the reason why I didn't see a problem was because
xfstests 299 was failing earlier on the baseline, and crashing my
regression tests.  So I simply commented it out just so I could
complete the testing.  It seems that xfstests 299 is problematic for
me, and I need to focus on how to make it pass successfully.  (Dmitry,
when I revert the commit which you identified, xfstests 299 is *still*
failing for me....) 

						- Ted

Re: EXT4 regression caused 4eec7

[Jan Kara]

On Mon 13-05-13 09:30:36, Ted Tso wrote:
> On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> > Grumble. In this case I think bitfields are not worth the trouble with gcc.
> > It's a pitty we have to spend additional 8 bytes for every journal_head but
> > we'll survive... I'll send Ted a partial revert and add a comment so that
> > we won't repeat this mistake in future.
> 
> Or just switch things to use explicit 32-bit boolean operations.
> Sounds the safest way to go is to simply not trust bitfields to be
> something gcc is competent to compile correctly, and just open code it
> in standard C.  (Large portions of ext4 and e2fsprogs do this
> manually, for historical reasons, and it sounds like we have a good
> reason to do it going forward.)
  Yeah, but in this case b_jlist testing / setting would require accessor
functions which is slightly ugly. For now I just submitted a revert of the
bitfield part and if someone feels like saving 8 bytes in struct
journal_head is worth the hassle, then we can later go that route.

> Jan, Dmitry --- I still have in my tree a revert for commit 4eec708d2:
> ext4: use io_end for multiple bios, since I belive Dmitry still
> bisected a regression for xfstests 299.  Dmitry, can you confirm that
> you are definitely seeing a regression here?  Jan, do you mind if we
> try to figure out how to fix this during the next development cycle,
> since it was part of your much longer, extensive patch series anyway?
  Yeah, for now just send a revert to Linus. I'll look into that failure
now but since I didn't hit the problem in my testing it may take a while.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: EXT4 regression caused 4eec7

[Dmitry Monakhov]

On Mon, 13 May 2013 09:30:36 -0400, Theodore Ts'o <tytso@mit.edu> wrote:
> On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> > Grumble. In this case I think bitfields are not worth the trouble with gcc.
> > It's a pitty we have to spend additional 8 bytes for every journal_head but
> > we'll survive... I'll send Ted a partial revert and add a comment so that
> > we won't repeat this mistake in future.
> 
> Or just switch things to use explicit 32-bit boolean operations.
> Sounds the safest way to go is to simply not trust bitfields to be
> something gcc is competent to compile correctly, and just open code it
> in standard C.  (Large portions of ext4 and e2fsprogs do this
> manually, for historical reasons, and it sounds like we have a good
> reason to do it going forward.)
> 
> Jan, Dmitry --- I still have in my tree a revert for commit 4eec708d2:
> ext4: use io_end for multiple bios, since I belive Dmitry still
> bisected a regression for xfstests 299.  Dmitry, can you confirm that
> you are definitely seeing a regression here?
Yes, this patch provoke use-after-free which detected by slab sanity checks.
>  Jan, do you mind if we
> try to figure out how to fix this during the next development cycle,
> since it was part of your much longer, extensive patch series anyway?
> 
> I've determined that the reason why I didn't see a problem was because
> xfstests 299 was failing earlier on the baseline, and crashing my
> regression tests. So I simply commented it out just so I could
> complete the testing.  It seems that xfstests 299 is problematic for
> me, and I need to focus on how to make it pass successfully.  (Dmitry,
> when I revert the commit which you identified, xfstests 299 is *still*
> failing for me....) 
In fact generic/299 always succeed for me, but it produce warning
WARNING: at fs/ext4/inode.c:3218 ext4_ext_direct_IO
and complains from slab debug. But it was missed because i've missed
this error in the logs and forget to check /proc/sys/kernel/tained.
> 
> 						- Ted
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: EXT4 regression caused 4eec7

[Theodore Ts'o]

On Mon, May 13, 2013 at 05:47:05PM +0400, Dmitry Monakhov wrote:
> In fact generic/299 always succeed for me, but it produce warning
> WARNING: at fs/ext4/inode.c:3218 ext4_ext_direct_IO
> and complains from slab debug. But it was missed because i've missed
> this error in the logs and forget to check /proc/sys/kernel/tained.

This is how it's failing for me....

generic/299		[23:06:27][  109.243220] fio (3376) used greatest stack depth: 5240 bytes left
[  109.252757] fio (3380) used greatest stack depth: 5140 bytes left
[  109.307227] fio (3374) used greatest stack depth: 4944 bytes left
 [23:08:10] [failed, exit status 1] - output mismatch (see /root/xfstests/results/generic/299.out.bad)
    --- tests/generic/299.out	2013-04-05 21:41:17.000000000 -0400
    +++ /root/xfstests/results/generic/299.out.bad	2013-05-11 23:08:10.835356876 -0400
    @@ -3,3 +3,6 @@
     Run fio with random aio-dio pattern
     
     Start fallocate/truncate loop
    +./common/rc: line 2055:  3335 Segmentation fault      "$@" >> $seqres.full 2>&1
    +failed: '/root/xfstests/bin/fio /tmp/3135-299.fio'
    +(see /root/xfstests/results/generic/299.full for details)
     ...
     (Run 'diff -u tests/generic/299.out /root/xfstests/results/generic/299.out.bad' to see the entire diff)

I haven't had a chance to investigate the core dump yet....

  	      	       	  	      	  - Ted

Re: Re: Re: EXT4 regression caused 4eec7

[Zheng Liu]

On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> On Sun 12-05-13 13:04:59, EUNBONG SONG wrote:
> > 
> > 
> > >> Since at this point it's safer to rollback the change and we can
> > >> investigate more deeply how to fix it correctly for the next
> > >> development cycle, this is the patch which I'm testing.
> > 
> > >>                     - Ted
> > 
> > > Hello, I've tested with your patch. But the same problem was reproduced.
> > > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> > 
> > Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> > ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
> > I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> > I don't know the root cause. 
>   This is really strange. I've verified the code and all the places
> modifying b_jlist or b_modified are holding bh_state lock so we should be
> safe...

Hi Jan,

Could you please take a look at this mail [1].  I don't think we hold
bh_state lock there.

1. http://www.spinics.net/lists/linux-ext4/msg38205.html

Thanks,
                                                - Zheng

Re: EXT4 regression caused 4eec7

[Dmitry Monakhov]

On Mon, 13 May 2013 09:52:21 -0400, Theodore Ts'o <tytso@mit.edu> wrote:
> On Mon, May 13, 2013 at 05:47:05PM +0400, Dmitry Monakhov wrote:
> > In fact generic/299 always succeed for me, but it produce warning
> > WARNING: at fs/ext4/inode.c:3218 ext4_ext_direct_IO
> > and complains from slab debug. But it was missed because i've missed
> > this error in the logs and forget to check /proc/sys/kernel/tained.
> 
> This is how it's failing for me....
Because you ask questions, but do not read answers :)
http://marc.info/?l=linux-ext4&m=136580060822252&w=2
http://marc.info/?l=linux-ext4&m=136610044500931&w=2
> 
> generic/299		[23:06:27][  109.243220] fio (3376) used greatest stack depth: 5240 bytes left
> [  109.252757] fio (3380) used greatest stack depth: 5140 bytes left
> [  109.307227] fio (3374) used greatest stack depth: 4944 bytes left
>  [23:08:10] [failed, exit status 1] - output mismatch (see /root/xfstests/results/generic/299.out.bad)
>     --- tests/generic/299.out	2013-04-05 21:41:17.000000000 -0400
>     +++ /root/xfstests/results/generic/299.out.bad	2013-05-11 23:08:10.835356876 -0400
>     @@ -3,3 +3,6 @@
>      Run fio with random aio-dio pattern
>      
>      Start fallocate/truncate loop
>     +./common/rc: line 2055:  3335 Segmentation fault      "$@" >> $seqres.full 2>&1
>     +failed: '/root/xfstests/bin/fio /tmp/3135-299.fio'
>     +(see /root/xfstests/results/generic/299.full for details)
>      ...
>      (Run 'diff -u tests/generic/299.out /root/xfstests/results/generic/299.out.bad' to see the entire diff)
> 
> I haven't had a chance to investigate the core dump yet....
> 
>   	      	       	  	      	  - Ted
> --
> 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: Re: Re: EXT4 regression caused 4eec7

[Jan Kara]

On Mon 13-05-13 21:56:43, Zheng Liu wrote:
> On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> > On Sun 12-05-13 13:04:59, EUNBONG SONG wrote:
> > > 
> > > 
> > > >> Since at this point it's safer to rollback the change and we can
> > > >> investigate more deeply how to fix it correctly for the next
> > > >> development cycle, this is the patch which I'm testing.
> > > 
> > > >>                     - Ted
> > > 
> > > > Hello, I've tested with your patch. But the same problem was reproduced.
> > > > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> > > 
> > > Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> > > ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
> > > I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> > > I don't know the root cause. 
> >   This is really strange. I've verified the code and all the places
> > modifying b_jlist or b_modified are holding bh_state lock so we should be
> > safe...
> 
> Hi Jan,
> 
> Could you please take a look at this mail [1].  I don't think we hold
> bh_state lock there.
> 
> 1. http://www.spinics.net/lists/linux-ext4/msg38205.html
  I'll also reply to that thread but: Yes, we don't hold bh_state lock when
reading b_jlist in that one case (that's why I wrote 'modify' and not just
'access' in my previous email). But that's really harmless since we don't
do any complex operations with b_jlist (only get & set) so we either see an
old value or a new one. And that particular use is going away anyway later
in my series.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: Re: Re: EXT4 regression caused 4eec7

[Zheng Liu]

On Mon, May 13, 2013 at 05:17:27PM +0200, Jan Kara wrote:
> On Mon 13-05-13 21:56:43, Zheng Liu wrote:
> > On Mon, May 13, 2013 at 03:18:09PM +0200, Jan Kara wrote:
> > > On Sun 12-05-13 13:04:59, EUNBONG SONG wrote:
> > > > 
> > > > 
> > > > >> Since at this point it's safer to rollback the change and we can
> > > > >> investigate more deeply how to fix it correctly for the next
> > > > >> development cycle, this is the patch which I'm testing.
> > > > 
> > > > >>                     - Ted
> > > > 
> > > > > Hello, I've tested with your patch. But the same problem was reproduced.
> > > > > Currently, I'm trying to git bisect. If i done git bisect, i will let you know.
> > > > 
> > > > Hi, I've done git bisect. and panic at jbd2_journal_put_journal_head() is caused by 
> > > > ae4647fb7654676fc44a97e86eb35f9f06b99f66: "jbd2: reduce journal_head size."
> > > > I write just code patch which revert ae4647fb7654676fc44a97e86eb35f9f06b99f66 because
> > > > I don't know the root cause. 
> > >   This is really strange. I've verified the code and all the places
> > > modifying b_jlist or b_modified are holding bh_state lock so we should be
> > > safe...
> > 
> > Hi Jan,
> > 
> > Could you please take a look at this mail [1].  I don't think we hold
> > bh_state lock there.
> > 
> > 1. http://www.spinics.net/lists/linux-ext4/msg38205.html
>   I'll also reply to that thread but: Yes, we don't hold bh_state lock when
> reading b_jlist in that one case (that's why I wrote 'modify' and not just
> 'access' in my previous email). But that's really harmless since we don't
> do any complex operations with b_jlist (only get & set) so we either see an
> old value or a new one. And that particular use is going away anyway later
> in my series.

I see.  Thanks for your explanation.

                                                - Zheng

Re: EXT4 regression caused 4eec7

[Theodore Ts'o]

On Mon, May 13, 2013 at 05:59:25PM +0400, Dmitry Monakhov wrote:
> > This is how it's failing for me....
> Because you ask questions, but do not read answers :)
> http://marc.info/?l=linux-ext4&m=136580060822252&w=2
> http://marc.info/?l=linux-ext4&m=136610044500931&w=2

Sorry, I thought I was running with the updated fio, but apparently I
was using an old xfstests.tar.gz tarball on my KVM image.  Mea culpa....

    	     	 		 	 - Ted