linux-kernel - Re: [Bug 10489] Kprobe smoke test lockdep warning

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Date:	Tue, 22 Apr 2008 18:05:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Adrian Bunk <bunk@...nel.org>, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	bugme-daemon@...zilla.kernel.org,
	jean-marc LACROIX <jeanmarc.lacroix@...e.Fr>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [Bug 10489] Kprobe smoke test lockdep warning

On Tue, 2008-04-22 at 11:25 -0400, Masami Hiramatsu wrote:
> Peter Zijlstra wrote:
> > On Tue, 2008-04-22 at 15:09 +0200, Peter Zijlstra wrote:
> >> On Mon, 2008-04-21 at 18:54 -0400, Masami Hiramatsu wrote:
> >>> Thank you for reporting.
> >>>
> >>> Actually, kprobes tries to fixup thread's flags in post_kprobe_handler
> >>> (which is called from kprobe_exceptions_notify) by
> >>> trace_hardirqs_fixup_flags(pt_regs->flags). However, even the irq flag
> >>> is set in pt_regs->flags, true hardirq is still off until returning
> >>> from do_debug. Thus, lockdep assumes that hardirq is off without annotation.
> > 
> > Ah, can you clarrify? pt_regs->flags will only be set when returning to
> > the original trap site? in that case we should not need a lockdep
> > annotation I guess, unless its allowed and exptected for the int3 site
> > to change IRQ state.
> 
> As far as I took a look at the lockdep, your suggestion is correct.
> post_kprobe_handler should not set a lockdep annotation, because
> processor's IF is not changed yet in that time.

That much was clear; but when _will_ it be changed?

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