On (Fri) 22 Aug 2014 [07:48:19], Paul E. McKenney wrote:
> On Fri, Aug 22, 2014 at 06:26:49PM +0530, Amit Shah wrote:
> > On (Fri) 22 Aug 2014 [18:06:51], Amit Shah wrote:
> > > On (Fri) 22 Aug 2014 [17:54:53], Amit Shah wrote:
> > > > On (Mon) 18 Aug 2014 [21:01:49], Paul E. McKenney wrote:
> > > >
> > > > > The odds are low over the next few days. I am adding nastier
> > > > > rcutorture
> > > > > testing, however. It would still be very good to get debug
> > > > > information
> > > > > from your setup. One approach would be to convert the trace function
> > > > > calls into printk(), if that would help.
> > > >
> > > > I added a few printks on the lines of the traces in cases where
> > > > rcu_nocb_poll was checked -- since that reproduces the hang. Are the
> > > > following traces sufficient, or should I keep adding more printks?
> > > >
> > > > In the case of rcu-trace-nopoll.txt, the messages stop after a while
> > > > (when the guest locks up hard). That's when I kill the qemu process.
> > >
> > > And this is bt from gdb when the endless
> > >
> > > RCUDEBUG __call_rcu_nocb_enqueue 2146 rcu_preempt 0 WakeNot
> > >
> > > messages are being spewed.
> > >
> > > I can't time it, but hope it gives some indication along with the printks.
> >
> > ... and after the system 'locks up', this is the state it's in:
> >
> > ^C
> > Program received signal SIGINT, Interrupt.
> > native_safe_halt () at ./arch/x86/include/asm/irqflags.h:50
> > 50 }
> > (gdb) bt
> > #0 native_safe_halt () at ./arch/x86/include/asm/irqflags.h:50
> > #1 0xffffffff8100b9c1 in arch_safe_halt () at
> > ./arch/x86/include/asm/paravirt.h:111
> > #2 default_idle () at arch/x86/kernel/process.c:311
> > #3 0xffffffff8100c107 in arch_cpu_idle () at arch/x86/kernel/process.c:302
> > #4 0xffffffff8106a25a in cpuidle_idle_call () at kernel/sched/idle.c:120
> > #5 cpu_idle_loop () at kernel/sched/idle.c:220
> > #6 cpu_startup_entry (state=<optimized out>) at kernel/sched/idle.c:268
> > #7 0xffffffff813e068b in rest_init () at init/main.c:418
> > #8 0xffffffff81a8cf5a in start_kernel () at init/main.c:680
> > #9 0xffffffff81a8c4ba in x86_64_start_reservations
> > (real_mode_data=<optimized out>) at arch/x86/kernel/head64.c:193
> > #10 0xffffffff81a8c607 in x86_64_start_kernel (real_mode_data=0x13f90
> > <cpu_lock_stats+29184> <error: Cannot access memory at address 0x13f90>)
> > at arch/x86/kernel/head64.c:182
> > #11 0x0000000000000000 in ?? ()
> >
> >
> > Wondering why it's doing this. Am stepping through
> > cpu_startup_entry() to see if I get any clues.
>
> This looks to me like normal behavior in the x86 ACPI idle loop.
> My guess is that the lockup is caused by indefinite blocking, in
> which case we would expect all the CPUs to be in the idle loop.
Hm, found it:
The stall happens in do_initcalls().
pm_sysrq_init() is the function that causes the hang. When I #if 0
the line
register_sysrq_key('o', &sysrq_poweroff_op);
in pm_sysrq_init(), the boot proceeds normally.
Now what this is, and what relation this has to rcu and that patch in
particular is next...
Amit
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
