Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1357035

Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic

Show all headers | View raw

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

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-08 15:40 +0100
  Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Christoph Lameter <cl@linux.com> - 2016-03-08 16:10 +0100
    Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <vgupta@synopsys.com> - 2016-03-08 16:50 +0100
      Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Christoph Lameter <cl@linux.com> - 2016-03-08 21:50 +0100
        Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-09 07:50 +0100
          Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-09 11:20 +0100
            Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-09 11:40 +0100
              Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-09 12:20 +0100
            Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-09 12:10 +0100
              Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-09 12:50 +0100
                Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-09 13:00 +0100
                Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-09 13:30 +0100
                Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-14 09:10 +0100
            Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-09 14:30 +0100
              Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-09 16:00 +0100
                Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-03-10 07:00 +0100
                Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Peter Zijlstra <peterz@infradead.org> - 2016-03-10 10:20 +0100
  Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic Vlastimil Babka <vbabka@suse.cz> - 2016-03-08 16:40 +0100

csiph-web