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

From Christoph Lameter <cl@linux.com>
Newsgroups linux.kernel
Subject Re: [PATCH] mm: slub: Ensure that slab_unlock() is atomic
Date 2016-03-08 21:50 +0100
Message-ID <rawJR-659-45@gated-at.bofh.it> (permalink)
References <raqXM-25J-23@gated-at.bofh.it> <rarqO-2vx-23@gated-at.bofh.it> <ras3w-2Le-35@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, 8 Mar 2016, Vineet Gupta wrote:

> # set the bit
> 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)

Duh. Guess you  need to take the spinlock also in the arch specific
implementation of __bit_spin_unlock(). This is certainly not the only case
in which we use the __ op to unlock.

You need a true atomic op or you need to take the "spinlock" in all
cases where you modify the bit. If you take the lock in __bit_spin_unlock
then the race cannot happen.

> Are you convinced now !

Yes, please fix your arch specific code.

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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

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