Re: [PATCH] Fix BUG: using smp_processor_id() in preemptible code in print_fatal_signal()

[Ingo Molnar <mingo@elte.hu>]

* Ed Swierk <eswierk@aristanetworks.com> wrote:

> On Tue, 2009-01-27 at 00:15 +0100, Ingo Molnar wrote:
> > This trades a (harmless) debug warning against a potential deadlock or 
> > even a crash, because print_fatal_signal() can do this:
> > 
> >                         __get_user(insn, (unsigned char *)(regs->ip + i));
> > 
> > which will work without a fault most of the time but might also generate a 
> > pagefault and schedule away from atomic context.
> 
> Ouch!
> 
> > So please add preempt_disable()+preempt_enable() calls around the 
> > show_regs() call instead.
> 
> Take 2:
> 
> With print-fatal-signals=1 on a kernel with CONFIG_PREEMPT=y, sending an
> unexpected signal to a process causes a BUG: using smp_processor_id() in
> preemptible code.
> 
> get_signal_to_deliver() releases the siglock before calling
> print_fatal_signal(), which calls show_regs(), which calls
> smp_processor_id(), which is not supposed to be called from a
> preemptible thread.
> 
> Signed-off-by: Ed Swierk <eswierk@aristanetworks.com>

applied to tip/core/urgent, thanks Ed!

You can track/test your fix via the -tip tree's tip/master branch:

  http://people.redhat.com/mingo/tip.git/README

	Ingo