linux-kernel - Re: Thread flags modified without set_thread

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Date:	Thu, 1 Mar 2007 10:34:51 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mathieu Desnoyers <compudj@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Thread flags modified without set_thread_flag() (non
 atomically)

[trimming cc list since I'm only replying to the avr32 part]

On Wed, 28 Feb 2007 22:03:49 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 26 Feb 2007 12:10:37 -0800 Mathieu Desnoyers <compudj@...gle.com> wrote:

> > avr32/kernel/ptrace.c:          ti->flags |= _TIF_BREAKPOINT;
> 
> No, I don't immediately see anything in the flush_old_exec() code path
> which tells us that nobody else can look up this thread_info (or be holding
> a ref to it) in this context.
> 
> 
> > avr32/kernel/ptrace.c:                  ti->flags |= TIF_SINGLE_STEP;
> 
> heh.  Haarvard, you got a bug.

Heh, yeah. That would indeed explain some strange gdb behaviour. It
will only trigger when single-stepping into an exception or interrupt
handler so thanks for pointing it out; I would have had a hard time
figuring it out on my own...

I don't think either of those need to be atomic though, since both of
them happen in monitor mode with interrupts disabled.

Haavard
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