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

[Mateusz Guzik]

Hi. This remains unfixed.

On 8/4/20, Emmanuel Vadot <manu at bidouilliste.com> wrote:
> 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>
>


-- 
Mateusz Guzik <mjguzik gmail.com>