From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@elte.hu>
Cc: John Stultz <john.stultz@linaro.org>,
LKML <linux-kernel@vger.kernel.org>,
Joe Perches <joe@perches.com>,
Michal Nazarewicz <mina86@mina86.com>,
Andy Whitcroft <apw@canonical.com>,
Jiri Slaby <jirislaby@gmail.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
David Rientjes <rientjes@google.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 1/3] comm: Introduce comm_lock spinlock to protect task->comm access
Date: Tue, 17 May 2011 23:54:16 +0200 [thread overview]
Message-ID: <1305669256.2466.6286.camel@twins> (raw)
In-Reply-To: <20110517212734.GB28054@elte.hu>
On Tue, 2011-05-17 at 23:27 +0200, Ingo Molnar wrote:
> * John Stultz <john.stultz@linaro.org> wrote:
>
> > The implicit rules for current->comm access being safe without locking are no
> > longer true. Accessing current->comm without holding the task lock may result
> > in null or incomplete strings (however, access won't run off the end of the
> > string).
>
> This is rather unfortunate - task->comm is used in a number of performance
> critical codepaths such as tracing.
>
> Why does this matter so much? A NULL string is not a big deal.
>
> Note, since task->comm is 16 bytes there's the CMPXCHG16B instruction on x86
> which could be used to update it atomically, should atomicity really be
> desired.
The changelog also fails to mention _WHY_ this is no longer true. Nor
does it treat why making it true again isn't an option.
Who is changing another task's comm? That's just silly.
next prev parent reply other threads:[~2011-05-17 21:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-17 20:47 [PATCH 0/3] v5 Improve task->comm locking situation John Stultz
2011-05-17 20:47 ` [PATCH 1/3] comm: Introduce comm_lock spinlock to protect task->comm access John Stultz
2011-05-17 21:27 ` Ingo Molnar
2011-05-17 21:54 ` Peter Zijlstra [this message]
2011-05-17 22:56 ` David Rientjes
2011-05-18 0:53 ` KOSAKI Motohiro
2011-05-17 22:27 ` John Stultz
2011-05-18 1:02 ` KOSAKI Motohiro
2011-05-17 20:47 ` [PATCH 2/3] printk: Add %ptc to safely print a task's comm John Stultz
2011-05-17 21:42 ` Jiri Slaby
2011-05-17 21:52 ` Joe Perches
2011-05-17 22:04 ` Jiri Slaby
2011-05-17 22:17 ` Joe Perches
2011-05-17 22:17 ` John Stultz
2011-05-17 20:47 ` [PATCH 3/3] checkpatch.pl: Add check for task comm references John Stultz
2011-05-17 20:58 ` Jiri Slaby
2011-05-17 21:04 ` Michal Nazarewicz
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