Hello Petr,
On (02/26/16 15:57), Petr Mladek wrote:
> On Fri 2016-02-26 12:37:20, Sergey Senozhatsky wrote:
> > When watchdog detects a hardlockup and calls nmi_panic() `printk_func'
> > must be restored via printk_nmi_exit() call, so panic() will be able
> > to flush nmi buf and show backtrace and panic message. We also better
> > explicitly ask nmi to printk_nmi_flush() in console_flush_on_panic(),
> > because it may be too late to rely on irq work.
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
> > ---
> > include/linux/kernel.h | 6 ++++--
> > kernel/printk/printk.c | 1 +
> > 2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index f4fa2b2..3ee33d5 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -469,10 +469,12 @@ do {
> > \
> > cpu = raw_smp_processor_id(); \
> > old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu); \
> > \
> > - if (old_cpu == PANIC_CPU_INVALID) \
> > + if (old_cpu == PANIC_CPU_INVALID) { \
> > + printk_nmi_exit(); \
>
> This might end up in a deadlock that printk_nmi() wanted to avoid.
aha, I see.
> I think about a compromise. We should try to get the messages
> out only when kdump is not enabled.
can we zap_locks() if we are on nmi_panic()->panic()->console_flush_on_panic()
path?
console_flush_on_panic() is happening after we send out smp_send_stop().
> PS: I am sorry for not responding much about the printk problems
> this week. I have attended a training and did not have much time
> for a real work.
no prob.
-ss
