Re: rcu: eqs related warnings in linux-next

[Frederic Weisbecker]

On Sat, Sep 29, 2012 at 06:37:37AM -0700, Paul E. McKenney wrote:
> On Sat, Sep 29, 2012 at 02:25:04PM +0200, Frederic Weisbecker wrote:
> > 2012/9/29 Sasha Levin <levinsasha928@xxxxxxxxx>:
> > > Maybe I could help here a bit.
> > >
> > > lappy linux # addr2line -i -e vmlinux ffffffff8111d45f
> > > /usr/src/linux/kernel/timer.c:549
> > > /usr/src/linux/include/linux/jump_label.h:101
> > > /usr/src/linux/include/trace/events/timer.h:44
> > > /usr/src/linux/kernel/timer.c:601
> > > /usr/src/linux/kernel/timer.c:734
> > > /usr/src/linux/kernel/timer.c:886
> > >
> > > Which means that it was about to:
> > >
> > >         debug_object_activate(timer, &timer_debug_descr);
> 
> Understood and agreed, hence my severe diagnostic patch.
> 
> > I can't find anything in the debug object code that might fault.
> > I was suspecting some per cpu allocated memory: per cpu allocation
> > sometimes use vmalloc
> > which uses lazy paging using faults. But I can't find such thing there.
> > 
> > May be there is some faulting specific to KVM...
> 
> Sasha, is the easily reproducible?  If so, could you please try the
> previous patch?  It will likely give us more information on where
> this bug really lives.  (Yes, it might totally obscure the bug, but
> in that case we will just need to try some other perturbation.)

Isn't your patch actually removing the timer? But if so, we won't fault
anymore, or may be you want to check if we fault also outside the timer?

Just in case, I'm posting a second patch that dumps the regs when we
fault in the middle of an RCU user mode API. This way we can find
the precise rip where we fault:

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