Date:	Wed, 29 Sep 2010 15:37:03 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org,
	rwheeler@...hat.com, sandeen@...hat.com, adilger@...ger.ca,
	snitzer@...il.com
Subject: Re: [PATCH 0/6 v4] Lazy itable initialization for Ext4

On Tue, 28 Sep 2010, Ted Ts'o wrote:

> On Thu, Sep 16, 2010 at 02:47:25PM +0200, Lukas Czerner wrote:
> > 
> > as Mike suggested I have rebased the patch #1 against Jens'
> > linux-2.6-block.git 'for-next' branch and changed sb_issue_zeroout()
> > to cope with the new blkdev_issue_zeroout(), and changed
> > sb_issue_zeroout() to the new syntax everywhere I am using it.
> > Also some typos gets fixed.
> 
> We may have a problem with the lazy_itable patches.  I've tried
> running the XFSTESTS three times now.  This was with a system where
> mke2fs was setup (via /etc/mke2fs.conf) to always format the file
> system using lazy_itable_init.  This meant that any of the xfstests
> which reformated the scratch partition and then started a stress test
> would stress the newly added itable initialization code.
> Unfortunately the results weren't good.
> 
> The first time, I got the following soft lockup warning:
> 
> [ 2520.528745] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 2520.531445]  ef2b8e44 00000046 00000007 e29c1500 e29c1500 e29c1760 e29c175c c0b55500
> [ 2520.534983]  c0b55500 e29c175c c0b55500 c0b55500 c0b55500 32423426 00000224 00000000
> [ 2520.538270]  00000224 e29c1500 00000001 ef205000 00000005 ef2b8e74 ef2b8e80 c026eb2c
> [ 2520.541743] Call Trace:
> [ 2520.542742]  [<c026eb2c>] jbd2_log_wait_commit+0x103/0x14f
> [ 2520.544291]  [<c01711dc>] ? autoremove_wake_function+0x0/0x34
> [ 2520.545816]  [<c026bf95>] jbd2_log_do_checkpoint+0x1a8/0x458
> [ 2520.547431]  [<c026f4ed>] jbd2_journal_destroy+0x107/0x1d3
> [ 2520.549602]  [<c01711dc>] ? autoremove_wake_function+0x0/0x34
> [ 2520.551100]  [<c0252bef>] ext4_put_super+0x78/0x2f7
> [ 2520.552798]  [<c01f3c3c>] generic_shutdown_super+0x47/0xb8
> [ 2520.554692]  [<c01f3ccf>] kill_block_super+0x22/0x36
> [ 2520.556470]  [<c01f3816>] deactivate_locked_super+0x22/0x3e
> [ 2520.558372]  [<c01f3bf1>] deactivate_super+0x3d/0x41
> [ 2520.560138]  [<c02057a9>] mntput_no_expire+0xb5/0xd8
> [ 2520.561880]  [<c0206609>] sys_umount+0x273/0x298
> [ 2520.563358]  [<c0206640>] sys_oldumount+0x12/0x14
> [ 2520.564952]  [<c0646715>] syscall_call+0x7/0xb
> [ 2520.566596] 3 locks held by umount/15126:
> [ 2520.568121]  #0:  (&type->s_umount_key#20){++++..}, at: [<c01f3bea>] deactivate_super+0x36/0x41
> [ 2520.571819]  #1:  (&type->s_lock_key#2){+.+...}, at: [<c01f3096>] lock_super+0x20/0x22
> [ 2520.574788]  #2:  (&journal->j_checkpoint_mutex){+.+...}, at: [<c026f4e6>] jbd2_journal_destroy+0x100/0x1d3
> 
> In addition, there were these mysterious error messages:
> 
> [ 2542.026996] ata1: lost interrupt (Status 0x50)
> [ 2542.029750] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
> [ 2542.032656] ata1.00: failed command: WRITE DMA
> [ 2542.034312] ata1.00: cmd ca/00:10:00:00:00/00:00:00:00:00/e0 tag 0 dma 8192 out
> [ 2542.034313]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
> [ 2542.039892] ata1.00: status: { DRDY }
> 
> Why are they strange?  Because this was running under KVM, and there
> were no underlying hardware problems in the host OS.

Hi Ted,

this is really strange. I have never seen anything like this and I have
tried running the xfstests several times on the patchset while I was
creating it. Unfortunately I am not able to reproduce those errors even
now. I am running 2.6.26-rc6 with real SSD device.

Maybe the one difference is that I am using 2.6.36-rc6, so there is old
sb_issue_discard() interface (no flags and gfp_mask in function definition).
 And it is before Christoph's "remove BLKDEV_IFL_WAIT" patch
(dd3932eddf428571762596e17b65f5dc92ca361b in Jens for-next branch).

I'll search further.

> 
> The other two times I got a hard hang at XFStests 219 and 83, and the
> system was caught in such a type look that magic-sysrq wasn't working
> correctly.

Are you sure about the test numbers ? 083 does not even run on ext4 it
is xfs specific.

> 
> I've XFStests in this setup before applying these patches, and things
> worked fine.  I'm currently rolling back the patches and trying
> another xfstests runs just to make sure the problem wasn't introduced
> by some patch, but for now, it looks there might be a problem
> somewhere.  And unfortunately, since it's not happening in a regular
> location or test, and the system is so badly locked up sysrq doesn't
> work, finding it may be intersting....
> 
> 					- Ted
> 
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