Subject: Re: linux-next: manual merge of the rcu tree with the modules and tip trees

From: Stephen Rothwell <[email-masked]>
Date: Wed, 24 Jun 2015 09:23:44 +1000

Hi Rusty,

On Thu, 28 May 2015 17:25:07 +1000 Stephen Rothwell <[email-masked]> wrote:
>
> Today's linux-next merge of the rcu tree got a conflict in
> include/linux/rcupdate.h between commits 0a04b0166929 ("rcu: Move
> lockless_dereference() out of rcupdate.h") from the modules tree and
> c1ad348b452a ("tick: Nohz: Rework next timer evaluation") from the tip
> tree and commits 7d0ae8086b82 ("rcu: Convert ACCESS_ONCE() to
> READ_ONCE() and WRITE_ONCE()") and 3382adbc1bb8 ("rcu: Eliminate a few
> CONFIG_RCU_NOCB_CPU_ALL #ifdefs") from the rcu tree.
> 
> I fixed it up (see below) and can carry the fix as necessary (no action
> is required).
> 
> I also had to add this merge fix patch:
> 
> From: Stephen Rothwell <[email-masked]>
> Date: Thu, 28 May 2015 17:20:58 +1000
> Subject: [PATCH] rcu: merge fix for Convert ACCESS_ONCE() to READ_ONCE() and
>  WRITE_ONCE()
> 
> Signed-off-by: Stephen Rothwell <[email-masked]>
> ---
>  include/linux/compiler.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index ba91e5c88a32..f7e7235f3a91 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -483,7 +483,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>   */
>  #define lockless_dereference(p) \
>  ({ \
> -	typeof(p) _________p1 = ACCESS_ONCE(p); \
> +	typeof(p) _________p1 = READ_ONCE(p); \
>  	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
>  	(_________p1); \
>  })
> -- 
> 2.1.4
> 
> -- 
> Cheers,
> Stephen Rothwell                    [email-masked]
> 
> diff --cc include/linux/rcupdate.h
> index ed5f66464ab3,3a4d1bf430b1..000000000000
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@@ -1140,13 -1063,13 +1050,13 @@@ static inline notrace void rcu_read_unl
>   #define kfree_rcu(ptr, rcu_head)					\
>   	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
>   
> - #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
> + #ifdef CONFIG_TINY_RCU
>  -static inline int rcu_needs_cpu(unsigned long *delta_jiffies)
>  +static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
>   {
>  -	*delta_jiffies = ULONG_MAX;
>  +	*nextevt = KTIME_MAX;
>   	return 0;
>   }
> - #endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
> + #endif /* #ifdef CONFIG_TINY_RCU */
>   
>   #if defined(CONFIG_RCU_NOCB_CPU_ALL)
>   static inline bool rcu_is_nocb_cpu(int cpu) { return true; }

The above resolutions are now needed when the modules tree is merged
into Linus' tree (as the tip and rcu parts have already been merged).

-- 
Cheers,
Stephen Rothwell                    [email-masked]