On Fri, 18 Jan 2013 00:46:14 +0100
Jan Kara <j...@suse.cz> wrote:
> On Thu 17-01-13 13:39:17, Andrew Morton wrote:
> > On Thu, 17 Jan 2013 22:04:42 +0100
> > Jan Kara <j...@suse.cz> wrote:
> >
> > > ...
> > >
> > > So I played a bit with this. To make things easier for me I added
> > > artificial mdelay(len*10) (effectively simulating console able to print
> > > 100
> > > characters per second) just after call_console_drivers() so that I can
> > > trigger issues even on a machine easily available to me. Booting actually
> > > doesn't trigger any problems because there aren't enough things happening
> > > in parallel on common machine during boot but
> > > echo t >/proc/sysrq-trigger &
> > > for i in /lib/modules/3.8.0-rc3-0-default/kernel/fs/*/*.ko; do
> > > name=`basename $i`; name=${name%.ko}; modprobe $name
> > > done
> > > easily triggers the problem (as modprobe uses both RCU & IPIs to signal
> > > all
> > > CPUs).
> > >
> > > Adding
> > > touch_nmi_watchdog();
> > > touch_all_softlockup_watchdogs();
> > > rcu_cpu_stall_reset();
> >
> > I'm not sure that touch_all_softlockup_watchdogs() is needed?
> > touch_nmi_watchdog() itself calls touch_softlockup_watchdog().
> It is. I've tried without it and the machine died a horrible death
> because softlockup reports added to already too heavy printk traffic. The
> problem is that CPU doing printing cannot handle IPIs thus if someone calls
> e.g. smp_call_function_many() that function will spin waiting for IPIs on
> all CPUs to finish. And that doesn't happen until printing is done so
> CPU doing smp_call_function_many() gets locked up as well.
erk. I trust we'll have a nice comment explaining this mechanism ;)
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