From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
linux-parisc@vger.kernel, Helge Deller <deller@gmx.de>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
"James E.J. Bottomley" <jejb@parisc-linux.org>,
Pekka Enberg <penberg@kernel.org>,
linux-mm@kvack.org, Noam Camus <noamc@ezchip.com>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-snps-arc@lists.infradead.org,
Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic
Date: Mon, 14 Mar 2016 13:35:20 +0530 [thread overview]
Message-ID: <56E670C0.7080901@synopsys.com> (raw)
Message-ID: <20160314080520.L4UVj8nHRxd2tpxpdbnDz_1yqcDfqNnmXWpRr8S6UlM@z> (raw)
In-Reply-To: <20160309114054.GJ6356@twins.programming.kicks-ass.net>
On Wednesday 09 March 2016 05:10 PM, Peter Zijlstra wrote:
> ---
> Subject: bitops: Do not default to __clear_bit() for __clear_bit_unlock()
>
> __clear_bit_unlock() is a special little snowflake. While it carries the
> non-atomic '__' prefix, it is specifically documented to pair with
> test_and_set_bit() and therefore should be 'somewhat' atomic.
>
> Therefore the generic implementation of __clear_bit_unlock() cannot use
> the fully non-atomic __clear_bit() as a default.
>
> If an arch is able to do better; is must provide an implementation of
> __clear_bit_unlock() itself.
>
> Specifically, this came up as a result of hackbench livelock'ing in
> slab_lock() on ARC with SMP + SLUB + !LLSC.
>
> The issue was incorrect pairing of atomic ops.
>
> slab_lock() -> bit_spin_lock() -> test_and_set_bit()
> slab_unlock() -> __bit_spin_unlock() -> __clear_bit()
>
> The non serializing __clear_bit() was getting "lost"
>
> 80543b8e: ld_s r2,[r13,0] <--- (A) Finds PG_locked is set
> 80543b90: or r3,r2,1 <--- (B) other core unlocks right here
> 80543b94: st_s r3,[r13,0] <--- (C) sets PG_locked (overwrites unlock)
>
> Fixes ARC STAR 9000817404 (and probably more).
>
> Cc: stable@vger.kernel.org
> Reported-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
> Tested-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Peter, I don't see this in linux-next yet. I'm hoping you will send it Linus' way
for 4.6-rc1.
Thx,
-Vineet
next prev parent reply other threads:[~2016-03-14 8:05 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1457447457-25878-1-git-send-email-vgupta@synopsys.com>
[not found] ` <alpine.DEB.2.20.1603080857360.4047@east.gentwo.org>
[not found] ` <56DEF3D3.6080008@synopsys.com>
[not found] ` <alpine.DEB.2.20.1603081438020.4268@east.gentwo.org>
2016-03-09 6:43 ` [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta
2016-03-09 6:43 ` Vineet Gupta
2016-03-09 10:13 ` Peter Zijlstra
2016-03-09 10:13 ` Peter Zijlstra
2016-03-09 10:31 ` Peter Zijlstra
2016-03-09 10:31 ` Peter Zijlstra
2016-03-09 11:12 ` Vineet Gupta
2016-03-09 11:00 ` Vineet Gupta
2016-03-09 11:40 ` Peter Zijlstra
2016-03-09 11:40 ` Peter Zijlstra
2016-03-09 11:53 ` Vineet Gupta
2016-03-09 12:22 ` Peter Zijlstra
2016-03-09 12:22 ` Peter Zijlstra
2016-03-14 8:05 ` Vineet Gupta [this message]
2016-03-14 8:05 ` Vineet Gupta
2016-03-09 13:22 ` Vineet Gupta
2016-03-09 13:22 ` Vineet Gupta
2016-03-09 14:51 ` Peter Zijlstra
2016-03-09 14:51 ` Peter Zijlstra
2016-03-10 5:51 ` Vineet Gupta
2016-03-10 9:10 ` Peter Zijlstra
2016-03-10 9:10 ` Peter Zijlstra
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