linux-kernel - Re: [PATCH 10/10] Use down_read_critical() for /sys/<pid>/exe and /sys/<pid>/maps files

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Date:	Thu, 20 May 2010 19:44:12 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 10/10] Use down_read_critical() for /sys/<pid>/exe and 
	/sys/<pid>/maps files

On Wed, May 19, 2010 at 8:21 AM, David Howells <dhowells@...hat.com> wrote:
>  0   0  10   2   1 s   2/2         0         0   2217200    636227    210255
>  0   0  10   2   1 s   2/2         0         0   2217903    629175    212926
>  0   0  10   2   1 s   2/2         0         0   2224136    647912    212506
>
> Feel free to have a play.

Thanks for sharing your testing code.

> BTW, the code also works on FRV in NOMMU mode (which uses the spinlock-based
> rwsem version).

Yes, I made sure to keep the generic (and non-x86 asm) versions
working by always separating x86 specific changes from the rest.

> However...  I'm not certain that giving a process that's accessing
> /proc/pid/maps priority over a second process that may be trying to do mmap or
> page fault or something internally is a good idea.

One thing to keep in mind if you're concerned about the higher
priority is that these /proc files are still not open to everyone - a
user can't read the /proc/<pid>/exe and /proc/<pid>/maps files for
another user's processes unless he's got CAP_SYS_PTRACE priviledges.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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