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Date: Sat, 15 Feb 2003 17:35:21 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: Andrew Morton <akpm@digeo.com>
cc: "Martin J. Bligh" <mbligh@aracnet.com>,
       Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Fw: 2.5.61 oops running SDET
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On Sat, 15 Feb 2003, Andrew Morton wrote:
>
> The recent change to fs/proc/array.c:task_sig()?
> 
>         buffer += sprintf(buffer, "ShdPnd:\t");
>         buffer = render_sigset_t(&p->signal->shared_pending.signal, buffer);

Yeah, but I think the bug has existed for much longer. 

It looks like "proc_pid_status()" doesn't actually lock the task at all, 
nor even bother to test whether the task has signal state. Which has 
_always_ been a bug. I don't know why it would start happening now, but it 
might just be unlucky timing.

I think the proper fix is to put a 

	task_lock()
	..
	task_unlock()

around the whole proc_pid_status() function, _and_ then verify that 
"tsk->sighand" is non-NULL.

(Oh, careful, that's already what "get_task_mm()" does internally, so look 
out for deadlocks - you'd need to open-code the get_task_mm() in there 
too, so the end result is something like

	task_lock(task)
	if (task->mm) {
		.. mm state
	}
	if (task->sighand) {
		.. signal state
	}
	..
	task_unlock(task);

instead).

		Linus

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