Re: [PATCH 26/35] [PATCH 26/36] powerpc: Replace __get_cpu_var uses

Alexander Graf
2014-12-16T22:07:14Z

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@kernel.crashing.org>
>> CC: Paul Mackerras <paulus@samba.org>
>> Signed-off-by: Christoph Lameter <cl@linux.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@suse.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@suse.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;