Re: [PATCH 2/2] locking/rwsem: Disable optimistic spinning for PA-RISC

Peter Zijlstra
2014-06-06T17:53:44Z

On Fri, Jun 06, 2014 at 10:22:21AM -0700, Linus Torvalds wrote:
> On Fri, Jun 6, 2014 at 10:11 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > +config ARCH_NO_ATOMIC_RMW
> > + def_bool y
> > + depends on PARISC || SPARC32 || METAG_ATOMICITY_LOCK1 || (TILE && !TILEGX) || (ARC && !ARC_HAS_LLSC)
>
> Ugh. We've had these kinds of things before, and they are broken and
> nasty to maintain.
>
> Just make it
>
> config ARCH_SUPPORTS_ATOMIC_RMW
> bool
>
> which defaults to no. And then make MUTEX_SPIN_ON_OWNER depend on that.

---
Subject: locking, mutex: Make optimistic spinning depend on ARCH_SUPPORTS_ATOMIC_RMW

The optimistic spin code assumes regular stores and cmpxchg() play nice;
this is found to not be true for at least: parisc, sparc32, tile32,
metag-lock1, arc-!llsc and hexagon.

There is further wreckage, but this in particular seemed easy to
trigger, so blacklist this.

Opt in for known good archs.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
arch/arm/Kconfig | 1 +
arch/arm64/Kconfig | 1 +
arch/powerpc/Kconfig | 1 +
arch/sparc/Kconfig | 1 +
arch/x86/Kconfig | 1 +
kernel/Kconfig.locks | 5 ++++-
6 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a2c1a18a7275..b8a6a5078eae 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -6,6 +6,7 @@ config ARM
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_HAVE_CUSTOM_GPIO_H
select ARCH_MIGHT_HAVE_PC_PARPORT
+ select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_WANT_IPC_PARSE_VERSION
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5c30b10c0f6c..339dc07f15e2 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -3,6 +3,7 @@ config ARM64
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
+ select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_WANT_OPTIONAL_GPIOLIB
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
select ARCH_WANT_FRAME_POINTERS
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e0998997943b..5bb96f282373 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -145,6 +145,7 @@ config PPC
select HAVE_IRQ_EXIT_ON_IRQ_STACK
select ARCH_USE_CMPXCHG_LOCKREF if PPC64
select HAVE_ARCH_AUDITSYSCALL
+ select ARCH_SUPPORTS_ATOMIC_RMW

config GENERIC_CSUM
def_bool CPU_LITTLE_ENDIAN
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 29f2e988c56a..407c87d9879a 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -78,6 +78,7 @@ config SPARC64
select HAVE_C_RECORDMCOUNT
select NO_BOOTMEM
select HAVE_ARCH_AUDITSYSCALL
+ select ARCH_SUPPORTS_ATOMIC_RMW

config ARCH_DEFCONFIG
string
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3d4951d35587..2fe1f7c5994e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -130,6 +130,7 @@ config X86
select HAVE_CC_STACKPROTECTOR
select GENERIC_CPU_AUTOPROBE
select HAVE_ARCH_AUDITSYSCALL
+ select ARCH_SUPPORTS_ATOMIC_RMW

config INSTRUCTION_DECODER
def_bool y
diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index d2b32ac27a39..ecee67a00f5f 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -220,6 +220,9 @@ config INLINE_WRITE_UNLOCK_IRQRESTORE

endif

+config ARCH_SUPPORTS_ATOMIC_RMW
+ bool
+
config MUTEX_SPIN_ON_OWNER
def_bool y
- depends on SMP && !DEBUG_MUTEXES
+ depends on SMP && !DEBUG_MUTEXES && ARCH_SUPPORTS_ATOMIC_RMW