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

[Peter Zijlstra]

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.

Hmm?