linux-kernel - Re: [PATCH 0/2] [GIT PULL] tracing: various bug fixes

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Date:	Thu, 23 Apr 2009 09:49:57 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/2] [GIT PULL] tracing: various bug fixes

Steven Rostedt wrote:
> Ah, this is a lockdep thing.
>
> The raw_local_irq_save/restore in __native_flush_tlb_global does not 
> update hardirqs_enabled.
>
> When we call into ftrace, when we cross page bounderies, we disable 
> interrupts using the normal local_irq_save/restore calls.
>
> But when we restore, it detects that interrupts are not going to be 
> enabled, and keeps hardirqs_enabled off.
>
> The printk solved the issue because it called local_irq_restore, which set 
> the variable back.
>
> I guess there's two solutions here. One, we can change the 
> raw_local_irq_enable/disable variants in __native_flush_tlb_global to the 
> non-raw type (it should protect against recursion).
>
> or we can try to make the ring buffer use the raw_local_irq variants too. 
> I tried this once before, and it did cause issues.
>
> Note, there's a "check_flags" in lockdep, but it is only called on 
> locking, it is not called when we only disable/enable interrupts.
>   

OK, the good news is that its not a callee-save calling convention 
problem, which is what I feared.  But it does sound pretty awkward to 
fix.  Does __native_flush_tlb_global() have to use 
raw_local_irq_save/restore?

    J
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