Re: [patch V2 28/29] stacktrace: Provide common infrastructure

[Peter Zijlstra]

On Fri, Apr 19, 2019 at 10:32:30AM +0200, Thomas Gleixner wrote:
> On Fri, 19 Apr 2019, Peter Zijlstra wrote:
> > On Thu, Apr 18, 2019 at 10:41:47AM +0200, Thomas Gleixner wrote:
> > 
> > > +typedef bool (*stack_trace_consume_fn)(void *cookie, unsigned long addr,
> > > +                                      bool reliable);
> > 
> > > +void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
> > > +		     struct task_struct *task, struct pt_regs *regs);
> > > +int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, void *cookie,
> > > +			     struct task_struct *task);
> > 
> > This bugs me a little; ideally the _reliable() thing would not exists.
> > 
> > Thomas said that the existing __save_stack_trace_reliable() is different
> > enough for the unification to be non-trivial, but maybe Josh can help
> > out?
> > 
> > >From what I can see the biggest significant differences are:
> > 
> >  - it looks at the regs sets on the stack and for FP bails early
> >  - bails for khreads and idle (after it does all the hard work!?!)
> > 
> > The first (FP checking for exceptions) should probably be reflected in
> > consume_fn(.reliable) anyway -- although that would mean a lot of extra
> > '?' entries where there are none today.
> > 
> > And the second (KTHREAD/IDLE) is something that the generic code can
> > easily do before calling into the arch unwinder.
> 
> And looking at the powerpc version of it, that has even more interesting
> extra checks in that function.

Right, but not fundamentally different from determining @reliable I
think.

Anyway, it would be good if someone knowledgable could have a look at
this.