Re: v6.12-rc workqueue lockups

[Dave Chinner <david@fromorbit.com>]

On Thu, Oct 24, 2024 at 10:35:29AM +0100, John Garry wrote:
> On 23/10/2024 21:39, Jan Kara wrote:
> > On Wed 23-10-24 11:19:24, John Garry wrote:
> > > Hi All,
> > > 
> > > I have been seeing lockups reliably occur on v6.12-rc1, 3, 4 and linus'
> > > master branch:
> > > 
> > > Message from syslogd@jgarry-atomic-write-exp-e4-8-instance-20231214-1221 at
> > > Oct 22 09:07:15 ...
> > >   kernel:watchdog: BUG: soft lockup - CPU#12 stuck for 26s! [khugepaged:154]
> > 
> > BTW, can you please share logs which would contain full stacktraces that
> > this softlockup reports produce? The attached dmesg is just from fresh
> > boot...  Thanks!
> > 
> 
> thanks for getting back to me.
> 
> So I think that enabling /proc/sys/kernel/softlockup_all_cpu_backtrace is
> required there. Unfortunately my VM often just locks up without any sign of
> life.

Attach a "serial" console to the vm - add "console=ttyS0,115600" to
the kernel command line and add "-serial pty" to the qemu command
line. You can then attach something like minicom to the /dev/pts/X
device that qemu creates for the console output and capture
everything from initial boot right through to the softlockup traces
that are emitted...

-Dave.
-- 
Dave Chinner
david@fromorbit.com