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

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Message-ID: <alpine.LNX.2.00.1605022159230.27942@cbobk.fhfr.pm>
Date:	Mon, 2 May 2016 22:00:42 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	live-patching@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Chris J Arges <chris.j.arges@...onical.com>,
	linuxppc-dev@...ts.ozlabs.org, Jessica Yu <jeyu@...hat.com>,
	Petr Mladek <pmladek@...e.com>, Jiri Slaby <jslaby@...e.cz>,
	Vojtech Pavlik <vojtech@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ
 tracking

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