linux-kernel - Re: [PATCH] binfmt_elf: core dump masking support

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Date:	Tue, 23 Jan 2007 09:08:39 +0000
From:	Pavel Machek <pavel@....cz>
To:	"Kawai, Hidehiro" <hidehiro.kawai.ez@...achi.com>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	gregkh@...e.de, james.bottomley@...eleye.com,
	Satoshi OSHIMA <soshima@...hat.com>,
	"Hideo AOKI@...hat" <haoki@...hat.com>,
	sugita <yumiko.sugita.yf@...achi.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] binfmt_elf: core dump masking support

On Tue 2007-01-23 13:42:00, Kawai, Hidehiro wrote:
> Hi,
> 
> >>>(run echo 1 > coremask, echo 0 > coremask in a loop while dumping
> >>>core. Do you have enough locking to make it work as expected?)
> >>
> >>Currently, any lock isn't acquired.  But I think the kernel only
> >>have to preserve the coremask setting in a local variable at the
> >>begining of core dumping.  I'm going to do this in the next version.
> > 
> > No, I do not think that is enough. At minimum, you'd need atomic_t
> > variable. But I'd recomend against it. Playing with locking is tricky.
> 
> Why do you think it is not enough?  I think that any locking is not
> needed.

You are wrong.

>   unsigned int mask = current->mm->coremask;

Not a valid C; coremask can change from another cpu.

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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