svn commit: r363842 - head/sys/compat/linuxkpi/common/include/linux

[Emmanuel Vadot]

On Tue, 4 Aug 2020 13:11:02 -0500
Alan Cox <alc at rice.edu> wrote:

> 
> On 8/4/20 10:25 AM, Emmanuel Vadot wrote:
> > Author: manu
> > Date: Tue Aug  4 15:25:22 2020
> > New Revision: 363842
> > URL: https://svnweb.freebsd.org/changeset/base/363842
> >
> > Log:
> >    linuxkpi: Add clear_bit_unlock
> >    
> >    This calls clear_bit and adds a memory barrier.
> >    
> >    Sponsored by: The FreeBSD Foundation
> >    
> >    Reviewed by:	hselasky
> >    MFC after:	1 week
> >    Differential Revision:	https://reviews.freebsd.org/D25943
> >
> > Modified:
> >    head/sys/compat/linuxkpi/common/include/linux/bitops.h
> >
> > Modified: head/sys/compat/linuxkpi/common/include/linux/bitops.h
> > ==============================================================================
> > --- head/sys/compat/linuxkpi/common/include/linux/bitops.h	Tue Aug  4 15:00:02 2020	(r363841)
> > +++ head/sys/compat/linuxkpi/common/include/linux/bitops.h	Tue Aug  4 15:25:22 2020	(r363842)
> > @@ -275,6 +275,13 @@ find_next_zero_bit(const unsigned long *addr, unsigned
> >   #define	test_bit(i, a)							\
> >       !!(READ_ONCE(((volatile const unsigned long *)(a))[BIT_WORD(i)]) & BIT_MASK(i))
> >   
> > +static inline void
> > +clear_bit_unlock(long bit, volatile unsigned long *var)
> > +{
> > +	clear_bit(bit, var);
> > +	wmb();
> 
> 
> For an unlock operation, the memory barrier should come before the 
> clear_bit() call, not after.  See, for example, the alpha implementation 
> in Linux.  Also, the correct "spelling" for this memory barrier in 
> FreeBSD would be atomic_thread_fence_rel(). See, for example, the 
> comment at the top of sys/amd64/include/atomic.h.

 Ah yes, thanks. I probably got lost looking for the linux implem but
that does make sense, I'll fix that probably tomorow.

 Thanks.

> 
> > +}
> > +
> >   static inline int
> >   test_and_clear_bit(long bit, volatile unsigned long *var)
> >   {


-- 
Emmanuel Vadot <manu at bidouilliste.com> <manu at freebsd.org>