Michael Holzheu <holzheu at linux.vnet.ibm.com> writes:
> Hello Eric,
>
> On Mon, 2011-10-24 at 10:07 -0700, Eric W. Biederman wrote:
>
> [snip]
>
>> So my second thought is to introduce another atomic variable
>> panic_in_progress, visible only in panic. The cpu that sets
>> increments panic_in_progress can call smp_send_stop. The rest of
>> the cpus can just go into a busy wait. That should stop nasty
>> fights about who is going to come out of smp_send_stop first.
>
> So this is a spinlock, no? What about the following patch:
Do we want both panic printks?
We really only need the mutual exclusion starting just before
smp_send_stop so that is where I would be inclined to put it.
But yeah something like the below should work.
Eric
> ---
> kernel/panic.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -59,6 +59,7 @@ EXPORT_SYMBOL(panic_blink);
> */
> NORET_TYPE void panic(const char * fmt, ...)
> {
> + static DEFINE_SPINLOCK(panic_lock);
> static char buf[1024];
> va_list args;
> long i, i_next = 0;
> @@ -68,8 +69,12 @@ NORET_TYPE void panic(const char * fmt,
> * It's possible to come here directly from a panic-assertion and
> * not have preempt disabled. Some functions called from here want
> * preempt to be disabled. No point enabling it later though...
> + *
> + * Only one CPU is allowed to execute the panic code. For multiple
> + * parallel invocations of panic all other CPUs will wait on the
> + * panic_lock. They are stopped afterwards by smp_send_stop().
> */
> - preempt_disable();
> + spin_lock(&panic_lock);
>
> console_verbose();
> bust_spinlocks(1);
