Message-ID: <1375967269.6848.46.camel@gandalf.local.home>
Subject: Re: [BUG] hackbench locks up with perf in 3.11-rc1 and beyond
From: Steven Rostedt <rostedt@goodmis.org>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameeter <cl@linux.com>,
        Wanpeng Li <liwanp@linux.vnet.ibm.com>,
        Pekka Enberg <penberg@kernel.org>
Date: Thu, 08 Aug 2013 09:07:49 -0400
In-Reply-To: <20130808050441.GA3214@lge.com>
References: <1375934936.6848.41.camel@gandalf.local.home>
	 <20130808050441.GA3214@lge.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1477
Lines: 45

On Thu, 2013-08-08 at 14:04 +0900, Joonsoo Kim wrote:

> Sorry about it.
> Now, I think that this is a buggy commit, so should be reverted.
> 
> For confirm that, could I ask a question about your configuration, Steven?
> I guess, you may set 0 to all kmem caches's cpu_partial via sysfs, doesn't it?

Ah, you're right. As this box is also used to test the -rt patch,
there's a script installed to disable all cpu_partials. This is because
cpu_partials are known to cause non-deterministic behavior in -rt.

I forgot about that script, as this box is used for regular mainline
testing as well.

> 
> In this case, memory leak is possible in following case.
> Code flow of possible leak is follwing case.
> 
> * in __slab_free()
> 1. (!new.inuse || !prior) && !was_frozen
> 2. !kmem_cache_debug && !prior
> 3. new.frozen = 1
> 4. after cmpxchg_double_slab, run the (!n) case with new.frozen=1
> 5. with this patch, put_cpu_partial() doesn't do anything,
> 	because this cache's cpu_partial is 0
> 6. return
> 
> In step 5, leak occur.
> 
> I have a solution to prevent this problem, but in this stage, IMHO,
> reverting it may be better.

Yeah, I would suggest that too. As this seems to be a serious
regression.

Thanks!

-- Steve

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/