linux-ext4 - Re: process hangs in ext4_sync

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Date:	Thu, 24 Oct 2013 11:54:36 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Sandeep Joshi <sanjos100@...il.com>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: process hangs in ext4_sync_file

On Wed, Oct 23, 2013 at 08:28:22PM +0530, Sandeep Joshi wrote:
> On Wed, Oct 23, 2013 at 3:50 PM, Jan Kara <jack@...e.cz> wrote:
> > On Mon 21-10-13 18:09:02, Sandeep Joshi wrote:
> >> I am seeing a problem reported 4 years earlier
> >> https://lkml.org/lkml/2009/3/12/226
> >> (same stack as seen by Alexander)
> >>
> >> The problem is reproducible.  Let me know if you need any info in
> >> addition to that seen below.
> >>
> >> I have multiple threads in a process doing heavy IO on a ext4
> >> filesystem mounted with (discard, noatime) on a SSD or HDD.
> >>
> >> This is on Linux 3.8.0-29-generic #42~precise1-Ubuntu SMP Wed Aug 14
> >> 16:19:23 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
> >>
> >> For upto minutes at a time, one of the threads seems to hang in sync to disk.
> >>
> >> When I check the thread stack in /proc, I find that the stack is one
> >> of the following two
> >>
> >> <ffffffff81134a4e>] sleep_on_page+0xe/0x20
> >> [<ffffffff81134c88>] wait_on_page_bit+0x78/0x80
> >> [<ffffffff81134d9c>] filemap_fdatawait_range+0x10c/0x1a0
> >> [<ffffffff811367d8>] filemap_write_and_wait_range+0x68/0x80
> >> [<ffffffff81236a4f>] ext4_sync_file+0x6f/0x2b0
> >> [<ffffffff811cba9b>] vfs_fsync+0x2b/0x40
> >> [<ffffffff81168fb3>] sys_msync+0x143/0x1d0
> >> [<ffffffff816fc8dd>] system_call_fastpath+0x1a/0x1f
> >> [<ffffffffffffffff>] 0xffffffffffffffff
> >>
> >>
> >> OR
> >>
> >>
> >> [<ffffffff812947f5>] jbd2_log_wait_commit+0xb5/0x130
> >> [<ffffffff81297213>] jbd2_complete_transaction+0x53/0x90
> >> [<ffffffff81236bcd>] ext4_sync_file+0x1ed/0x2b0
> >> [<ffffffff811cba9b>] vfs_fsync+0x2b/0x40
> >> [<ffffffff81168fb3>] sys_msync+0x143/0x1d0
> >> [<ffffffff816fc8dd>] system_call_fastpath+0x1a/0x1f
> >> [<ffffffffffffffff>] 0xffffffffffffffff
> >>
> >> Any clues?
> >   We are waiting for IO to complete. As the first thing, try to remount
> > your filesystem without 'discard' mount option. That is often causing
> > problems.
> >
> >                                                                 Honza
> 
> 
> Thanks Jan,  I will remove it and see what happens.
> I was also planning to switch to ext2 and see if the failure continues.
> I added the discard option because the filesystem was initially
> supposed to be on an SSD
> 
> is there any document which tells me what to look for in the output of
> "echo w > /proc/sysrq-trigger" ?

Sorry for the late.  Here it is [1].  I want to look at which process is
blocked.  Please try the testing as Jan suggested.

1. http://lxr.free-electrons.com/source/Documentation/sysrq.txt

Regards,
                                                - Zheng
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