linux-kernel - Re: Thread flags modified without set_thread

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Date:	Thu, 1 Mar 2007 00:17:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	compudj@...gle.com, mbligh@...gle.com,
	linux-kernel@...r.kernel.org, ak@...e.de, paulus@...ba.org,
	tony.luck@...el.com, hskinnemoen@...el.com
Subject: Re: Thread flags modified without set_thread_flag() (non
 atomically)

On Wed, 28 Feb 2007 22:23:41 -0800 (PST) David Miller <davem@...emloft.net> wrote:

> > That all looks rather deliberate.
> > 
> > > powerpc/kernel/process.c:               t->flags ^= (_TIF_ABI_PENDING | 
> > > _TIF_32BIT);
> > >
> > > ia64/kernel/mca.c:      ti->flags = _TIF_MCA_INIT;
> > >
> > > 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.
> 
> Provide the counter example, what other threads of control can modify
> relevant flags while a thread is exec()'ing?  It's essentially frozen
> outside of these code paths, otherwise we wouldn't be able to make all
> of these modifications to the task state.

As Mathieu points out, resched_task(), perhaps.  It can be called from interrupt.
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