Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking

Jiri Kosina
2016-05-02T20:00:53Z

On Mon, 2 May 2016, Jiri Kosina wrote:

> > FWIW, I just tried this:
> >
> > static bool is_entry_text(unsigned long addr)
> > {
> > return addr >= (unsigned long)__entry_text_start &&
> > addr < (unsigned long)__entry_text_end;
> > }
> >
> > it works. So the entry code is already annotated reasonably well :)
> >
> > I just hacked it up here:
> >
> > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=stack&id=085eacfe0edfc18768e48340084415dba9a6bd21
> >
> > and it seems to work, at least for page faults. A better
> > implementation would print out the entire contents of pt_regs so that
> > people reading the stack trace will know the registers at the time of
> > the exception, which might be helpful.
>
> Sorry for being dense, but how do you distinguish here between a "real"
> kernel entry, that pushes pt_regs, and any "non-entry" function call that
> passes pt_regs around?

Umm, actually, the more tricky part is the other way around -- how do you
make sure that whenever you are calling out from a code between
__entry_text_start and __entry_text_end, pt_regs will be at the place
you're looking for it? How's that guaranteed?

Thanks,

--
Jiri Kosina
SUSE Labs