On Tue, Apr 21, 2015 at 01:45:35PM +0930, Rusty Russell wrote:
> Aaro Koskinen <aaro.koskinen@xxxxxx> writes:
> > Hi,
> >
> > On Mon, Apr 20, 2015 at 12:40:28PM -0700, Guenter Roeck wrote:
> >> the upstream kernel fails to build mips:nlm_xlp_defconfig,
> >> mips:nlm_xlp_defconfig, mips:cavium_octeon_defconfig, and possibly
> >> other targets, with errors such as
> >>
> >> arch/mips/kernel/smp.c:211:2: error:
> >> passing argument 2 of 'cpumask_set_cpu' discards 'volatile' qualifier
> >> from pointer target type
> >> arch/mips/kernel/process.c:52:2: error:
> >> passing argument 2 of 'cpumask_test_cpu' discards 'volatile' qualifier
> >> from pointer target type
> >> arch/mips/cavium-octeon/smp.c:242:2: error:
> >> passing argument 2 of 'cpumask_clear_cpu' discards 'volatile' qualifier
> >> from pointer target type
> >>
> >> The problem was introduced with commit 8dd928915a73 (" mips: fix up
> >> obsolete cpu function usage"). I would send a patch to fix it, but I
> >> am not sure if removing 'volatile' from the variable declaration(s)
> >> would be a good idea.
> >
> > I think removing volatile from cpu_callin_map declaration should be OK,
> > since test_cpu (only reader) uses test_bit which takes care of it:
> >
> > static inline int test_bit(int nr, const volatile unsigned long *addr)
>
> No, that got replaced too, with cpumask_test_cpu AFAICT.
>
> You can open-code it, like so:
>
> test_bit(0, cpumask_bits(cpu_callin_map));
>
> But you probably want to put a barrier in that loop instead of relying
> on volatile.
>
The following might do it. Note that I can not really test it since I don't have
a real mips system, and qemu gets rcu hangs if I enable more than one CPU (I see
that with older kernels as well, so it is not a new problem). Someone will have
to test the patch on a real multi-core system.
Guenter
---
>From 94026cc98a6b7b3567780a5443674c71202e2497 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux@xxxxxxxxxxxx>
Date: Tue, 21 Apr 2015 08:31:01 -0700
Subject: [PATCH] mips: Fix SMP builds
Mips SMP builds fail with error messages similar to the following.
arch/mips/kernel/smp.c:211:2: error:
passing argument 2 of 'cpumask_set_cpu' discards 'volatile'
qualifier from pointer target type
arch/mips/kernel/process.c:52:2: error:
passing argument 2 of 'cpumask_test_cpu' discards 'volatile'
qualifier from pointer target type
arch/mips/cavium-octeon/smp.c:242:2: error:
passing argument 2 of 'cpumask_clear_cpu' discards 'volatile'
qualifier from pointer target type
cpu_callin_map is declared as volatile variable, but passed to various
functions with non-volatile arguments. Make it non-volatile and add a
memory barrier at the one location where volatile might be needed.
Fixes: 8dd928915a73 ("mips: fix up obsolete cpu function usage")
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
arch/mips/include/asm/smp.h | 2 +-
arch/mips/kernel/smp.c | 6 ++++--
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
index bb02fac9b4fa..2b25d1ba1ea0 100644
--- a/arch/mips/include/asm/smp.h
+++ b/arch/mips/include/asm/smp.h
@@ -45,7 +45,7 @@ extern int __cpu_logical_map[NR_CPUS];
#define SMP_DUMP 0x8
#define SMP_ASK_C0COUNT 0x10
-extern volatile cpumask_t cpu_callin_map;
+extern cpumask_t cpu_callin_map;
/* Mask of CPUs which are currently definitely operating coherently */
extern cpumask_t cpu_coherent_mask;
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 193ace7955fb..158191394770 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -43,7 +43,7 @@
#include <asm/time.h>
#include <asm/setup.h>
-volatile cpumask_t cpu_callin_map; /* Bitmask of started secondaries */
+cpumask_t cpu_callin_map; /* Bitmask of started secondaries */
int __cpu_number_map[NR_CPUS]; /* Map physical to logical */
EXPORT_SYMBOL(__cpu_number_map);
@@ -218,8 +218,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
/*
* Trust is futile. We should really have timeouts ...
*/
- while (!cpumask_test_cpu(cpu, &cpu_callin_map))
+ while (!cpumask_test_cpu(cpu, &cpu_callin_map)) {
udelay(100);
+ mb();
+ }
synchronise_count_master(cpu);
return 0;
--
2.1.0
