linux-kernel - Re: [PATCH 26/35] [PATCH 26/36] powerpc: Replace __get_cpu

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Date:	Tue, 16 Dec 2014 23:07:05 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>
CC:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Scott Wood <scottwood@...escale.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 26/35] [PATCH 26/36] powerpc: Replace __get_cpu_var uses

On 26.08.14 20:14, Tejun Heo wrote:
> On Sun, Aug 17, 2014 at 12:30:49PM -0500, Christoph Lameter wrote:
>> __get_cpu_var() is used for multiple purposes in the kernel source. One of
>> them is address calculation via the form &__get_cpu_var(x).  This calculates
>> the address for the instance of the percpu variable of the current processor
>> based on an offset.
>>
>> Other use cases are for storing and retrieving data from the current
>> processors percpu area.  __get_cpu_var() can be used as an lvalue when
>> writing data or on the right side of an assignment.
> ...
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> CC: Paul Mackerras <paulus@...ba.org>
>> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 
> (Please disregard the ones I posted for v1 of the patch series)
> 
> Applied to percpu/for-3.18-consistent-ops with the fix up patch rolled
> in.  Please let me know if this patch should be routed differently.
> Note that this patch was to be applied to percpu/for-3.17 but delayed
> due to build issues caused by cpumask_var_t.

Unfortunately this commit breaks e500v2 builds with KVM enabled:

  arch/powerpc/kvm/e500.c: In function "local_sid_setup_one":
  arch/powerpc/kvm/e500.c:81:29: error: macro "__this_cpu_write"
requires 2 arguments, but only 1 given
  arch/powerpc/kvm/e500.c:81:3: error: unknown type name "__this_cpu_write"
  arch/powerpc/kvm/e500.c:81:47: error: expected "=", ",", ";", "asm" or
"__attribute__" before ")" token
  arch/powerpc/kvm/e500.c:82:8: error: request for member "val" in
something not a structure or union
  arch/powerpc/kvm/e500.c:83:8: error: request for member "pentry" in
something not a structure or union

Looking at the offending line of code I'm not surprised:

-               __get_cpu_var(pcpu_sids).entry[sid] = entry;
+               __this_cpu_write(pcpu_sids)entry[sid], entry);

This doesn't quite look like valid C to me. The patch below fixes the
build error for me. Please check whether it's correct and if so apply it
directly to the tree.


Alex


From: Alexander Graf <agraf@...e.de>
Date: Tue, 16 Dec 2014 23:04:01 +0100
Subject: [PATCH] KVM: PPC: E500: Compile fix in this_cpu_write

Commit 69111bac42f5 (powerpc: Replace __get_cpu_var uses) introduced compile
breakage to the e500 target by introducing invalid automatically created C
syntax.

Fix up the breakage and make the code compile again.

Signed-off-by: Alexander Graf <agraf@...e.de>

diff --git a/arch/powerpc/kvm/e500.c b/arch/powerpc/kvm/e500.c
index 1609584..e1cb588 100644
--- a/arch/powerpc/kvm/e500.c
+++ b/arch/powerpc/kvm/e500.c
@@ -78,7 +78,7 @@ static inline int local_sid_setup_one(struct id *entry)

 	sid = __this_cpu_inc_return(pcpu_last_used_sid);
 	if (sid < NUM_TIDS) {
-		__this_cpu_write(pcpu_sids)entry[sid], entry);
+		__this_cpu_write(pcpu_sids.entry[sid], entry);
 		entry->val = sid;
 		entry->pentry = this_cpu_ptr(&pcpu_sids.entry[sid]);
 		ret = sid;
--
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