linux-kernel - Re: [PATCH 0/6] enable writing to /proc/pid/mem

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Message-ID: <20110309024708.GA4941@fibrous.localdomain>
Date:	Tue, 8 Mar 2011 21:47:08 -0500
From:	Stephen Wilson <wilsons@...rt.ca>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Roland McGrath <roland@...hat.com>,
	Matt Mackall <mpm@...enic.com>,
	David Rientjes <rientjes@...gle.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mel@....ul.ie>, Ingo Molnar <mingo@...e.hu>,
	Michel Lespinasse <walken@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] enable writing to /proc/pid/mem

On Wed, Mar 09, 2011 at 02:33:04AM +0000, Al Viro wrote:
> On Tue, Mar 08, 2011 at 09:15:25PM -0500, Stephen Wilson wrote:
> 
> > I think we could also remove the intermediate copy in both mem_read() and
> > mem_write() as well, but I think such optimizations could be left for
> > follow on patches.
> 
> How?  We do copy_.._user() in there; it can trigger page faults and
> that's not something you want while holding mmap_sem on some mm.

Ah, OK.   I did not think thru that subtlety.  Was merely mentioning
"things we might do afterwords" as opposed to a genuine proposal.

> Looks like a deadlock country...  So we can't do that from inside
> access_process_vm() or its analogs, which means buffering in caller.

Thanks for the feed back -- I am certainly (relatively speaking) new to
the code so your insights are most valuable.

Thanks again!


-- 
steve

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