linux-kernel - Re: How do I increment a per-CPU variable without warning?

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Date:	Wed, 16 Apr 2014 10:12:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, tj@...nel.org,
	grygorii.strashko@...com, peterz@...radead.org
Subject: Re: How do I increment a per-CPU variable without warning?

On Wed, Apr 16, 2014 at 09:06:21AM -0700, Paul E. McKenney wrote:
> On Wed, Apr 16, 2014 at 10:08:03AM -0500, Christoph Lameter wrote:
> > On Tue, 15 Apr 2014, Paul E. McKenney wrote:
> > 
> > > Hello, Christoph,
> > >
> > > I have a patch that currently uses __this_cpu_inc_return() to increment a
> > > per-CPU variable, but without preemption disabled.  Of course, given that
> > > preemption is enabled, it might well end up picking up one CPU's counter,
> > > adding one to it, then storing the result into some other CPU's counter.
> > > But this is OK, the test can be probabilistic.  And when I run this
> > > against v3.14 and earlier, it works fine.
> > 
> > We introduced raw_cpu_inc_return to squish these warnings.
> 
> Cool, this is a good short-term fix.

Or at least it is given the following patch.  Was this the intent?

							Thanx, Paul

------------------------------------------------------------------------

percpu: Fix raw_cpu_inc_return()

The definition for raw_cpu_add_return() uses the operation prefix
"raw_add_return_", but the definitions in the various percpu.h files
expect "raw_cpu_add_return_".  This commit therefore appropriately
adjusts the definition of raw_cpu_add_return().

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Christoph Lameter <cl@...ux.com>

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index e7a0b95ed527..495c6543a8f2 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -639,7 +639,7 @@ do {									\
 #  define raw_cpu_add_return_8(pcp, val)	raw_cpu_generic_add_return(pcp, val)
 # endif
 # define raw_cpu_add_return(pcp, val)	\
-	__pcpu_size_call_return2(raw_add_return_, pcp, val)
+	__pcpu_size_call_return2(raw_cpu_add_return_, pcp, val)
 #endif
 
 #define raw_cpu_sub_return(pcp, val)	raw_cpu_add_return(pcp, -(typeof(pcp))(val))

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