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

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Date:	Wed, 24 Jun 2015 09:39:02 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus <torvalds@...ux-foundation.org>
Subject: Re: linux-next: manual merge of the rcu tree with the modules and tip trees

Stephen Rothwell <sfr@...b.auug.org.au> writes:
> Hi Rusty,
>
> On Thu, 28 May 2015 17:25:07 +1000 Stephen Rothwell <sfr@...b.auug.org.au> 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 <sfr@...b.auug.org.au>
>> 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 <sfr@...b.auug.org.au>
>> ---
>>  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); \
>>  })

Good catch.  I've apply this to my modules-next tree now, as it will
work fine pre-merge.

Thanks,
Rusty.
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