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

[Jiri Kosina]

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