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Subject: Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered
	unnecessarily
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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Date: Tue, 24 Jul 2007 17:55:12 -0400
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On Wed, 2007-07-25 at 07:37 +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2007-07-24 at 11:13 -0700, Linus Torvalds wrote:
> > 
> > IOW, if you do a spinlock with the bitops, the locking side should be
> > able 
> > to use a "test_and_set_bit()" on its own, but the unlocking side
> > should be
> > 
> >         smp_mb__before_clear_bit();
> >         clear_bit();
> > 
> > because the ones that don't return a value also don't imply a memory 
> > barrier.
> 
> Yup. But I much prefer Nick's clear_bit_unlock() :-)
> 
> Ben

If you want to use bitops as spinlocks you should rather be using
<linux/bit_spinlock.h>. That also does the right thing w.r.t.
pre-emption and sparse locking annotations.

Trond