linux-kernel - Re: [PATCH -mm] select_bad_process: cleanup 'releasing' check

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Date:	Mon, 28 Aug 2006 19:00:03 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] select_bad_process: cleanup 'releasing' check

On 08/28, Nick Piggin wrote:
>
> On Sun, Aug 27, 2006 at 10:25:38PM +0400, Oleg Nesterov wrote:
> > 
> > -		releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
> > -						p->flags & PF_EXITING;
> > -		if (releasing) {
> > -			if (p->flags & PF_EXITING && p == current) {
> > -				chosen = p;
> > -				*ppoints = ULONG_MAX;
> > -				break;
> > -			}
> > -			return ERR_PTR(-1UL);
> > -		}
> > +		if ((p->flags & PF_EXITING) && p == current) {
> > +			chosen = p;
> > +			*ppoints = ULONG_MAX;
> > +			break;
> > +		}
> > +		if ((p->flags & PF_EXITING) ||
> > +				test_tsk_thread_flag(p, TIF_MEMDIE))
> > +			return ERR_PTR(-1UL);
> > +
> 
> Hmm, actually I think I spot a bug in the original logic: we don't want
> to have more than 1 task with TIF_MEMDIE at once, becaues that gives it
> access to memory reserves (but I saw it first in the new formulation, so
> maybe that does suggest it is more readable ;)
> 
> What I think should be done is the check for TIF_MEMDIE (and return -1)
> first, and then the PF_EXITING test. At which point, if current is found to
> be exiting, it should be chosen but not break... that way a subsequent MEMDIE
> or EXITING task has the chance to trigger the -1 return.

Aha! The logic looked somewhat strange to me, but ...

> Anyway, if you don't want to do all that, I will when my hand gets better.

I have little understanding of this magic, i'd better not to try to fix it.

> Otherwise the 3 patches you sent look good, they could all have an
> 
> Acked-by: Nick Piggin <npiggin@...e.de>

Thanks!

Oleg.

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