linux-ext4 - Re: Tasks stuck jbd2 for a long time

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Date:   Wed, 16 Aug 2023 16:53:10 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Bhatnagar, Rishabh" <risbhat@...zon.com>
Cc:     Theodore Ts'o <tytso@....edu>, jack@...e.com,
        linux-ext4@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Park, SeongJae" <sjpark@...zon.com>
Subject: Re: Tasks stuck jbd2 for a long time

On Tue 15-08-23 20:57:14, Bhatnagar, Rishabh wrote:
> On 8/15/23 7:28 PM, Theodore Ts'o wrote:
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> > 
> > 
> > 
> > It would be helpful if you can translate address in the stack trace to
> > line numbers.  See [1] and the script in
> > ./scripts/decode_stacktrace.sh in the kernel sources.  (It is
> > referenced in the web page at [1].)
> > 
> > [1] https://docs.kernel.org/admin-guide/bug-hunting.html
> > 
> > Of course, in order to interpret the line numbers, we'll need a
> > pointer to the git repo of your kernel sources and the git commit ID
> > you were using that presumably corresponds to 5.10.184-175.731.amzn2.x86_64.
> > 
> > The stack trace for which I am particularly interested is the one for
> > the jbd2/md0-8 task, e.g.:
> 
> Thanks for checking Ted.
> 
> We don't have fast_commit feature enabled. So it should correspond to this
> line:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/fs/jbd2/commit.c?h=linux-5.10.y#n496
> 
> > 
> > >        Not tainted 5.10.184-175.731.amzn2.x86_64 #1
> > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > task:jbd2/md0-8      state:D stack:    0 pid: 8068 ppid:     2
> > > flags:0x00004080
> > > Call Trace:
> > > __schedule+0x1f9/0x660
> > >   schedule+0x46/0xb0
> > >   jbd2_journal_commit_transaction+0x35d/0x1880 [jbd2]  <--------- line #?
> > >   ? update_load_avg+0x7a/0x5d0
> > >   ? add_wait_queue_exclusive+0x70/0x70
> > >   ? lock_timer_base+0x61/0x80
> > >   ? kjournald2+0xcf/0x360 [jbd2]
> > >   kjournald2+0xcf/0x360 [jbd2]
> > Most of the other stack traces you refenced are tasks that are waiting
> > for the transaction commit to complete so they can proceed with some
> > file system operation.  The stack traces which have
> > start_this_handle() in them are examples of this going on.  Stack
> > traces of tasks that do *not* have start_this_handle() would be
> > specially interesting.
> I see all other stacks apart from kjournald have "start_this_handle".

That would be strange. Can you post full output of "echo w
>/proc/sysrq-trigger" to dmesg, ideally passed through scripts/faddr2line as
Ted suggests. Thanks!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR