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

[Alan Cox]

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.


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