linux-kernel - Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external to a process (v7)

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Message-ID: <4AF7D8C2.60807@gmail.com>
Date:	Mon, 09 Nov 2009 09:54:26 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Neil Horman <nhorman@...driver.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external
 to a process (v7)

On 11/06/2009 10:26 AM, Ingo Molnar wrote:
> Also, the locking there looks messy:
> 
> +       /* optimization: 'current' doesn't need locking, e.g. setrlimit */
> +       if (tsk != current) {
> +               /* protect tsk->signal and tsk->sighand from disappearing */
> +               read_lock(&tasklist_lock);
> +               if (!tsk->sighand) {
> +                       retval = -ESRCH;
> +                       goto out;
> +               }
>         }
> 
> Neil's splitup into a helper function looks _far_ cleaner.

Oops, I don't understand here. Looking at
http://patchwork.kernel.org/patch/54863/
and
http://decibel.fi.muni.cz/cgi-bin/gitweb.cgi?p=linux.git;a=commitdiff;h=ba9ba971a9241250646091935d77d2f31b7c15af

They are almost identical. That 'if' above is added by:
http://decibel.fi.muni.cz/cgi-bin/gitweb.cgi?p=linux.git;a=commitdiff;h=bab65b1e6c0fd797a1ecdb32911faa82947effd0

The latter commit is to avoid performance penalty introduced for
setrlimit syscall by the added lock (as it's unneeded for 'current'). If
you find that crappy, there is no problem to drop it, indeed.
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