[PATCH -v4 5/7] locking, arch: Update spin_unlock_wait()
From: Peter Zijlstra
Date: Thu Jun 02 2016 - 07:58:34 EST
This patch updates/fixes all spin_unlock_wait() implementations.
The update is in semantics; where it previously was only a control
dependency, we now upgrade to a full load-acquire to match the
store-release from the spin_unlock() we waited on. This ensures that
when spin_unlock_wait() returns, we're guaranteed to observe the full
critical section we waited on.
This fixes a number of spin_unlock_wait() users that (not
unreasonably) rely on this.
I also fixed a number of ticket lock versions to only wait on the
current lock holder, instead of for a full unlock, as this is
sufficient.
Furthermore; again for ticket locks; I added an smp_rmb() in between
the initial ticket load and the spin loop testing the current value
because I could not convince myself the address dependency is
sufficient, esp. if the loads are of different sizes.
I'm more than happy to remove this smp_rmb() again if people are
certain the address dependency does indeed work as expected.
Cc: jejb@xxxxxxxxxxxxxxxx
Cc: davem@xxxxxxxxxxxxx
Cc: chris@xxxxxxxxxx
Cc: rth@xxxxxxxxxxx
Cc: dhowells@xxxxxxxxxx
Cc: schwidefsky@xxxxxxxxxx
Cc: mpe@xxxxxxxxxxxxxx
Cc: ralf@xxxxxxxxxxxxxx
Cc: linux@xxxxxxxxxxxxxxx
Cc: rkuo@xxxxxxxxxxxxxx
Cc: vgupta@xxxxxxxxxxxx
Cc: james.hogan@xxxxxxxxxx
Cc: realmz6@xxxxxxxxx
Cc: ysato@xxxxxxxxxxxxxxxxxxxx
Cc: tony.luck@xxxxxxxxx
Cc: cmetcalf@xxxxxxxxxxxx
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/alpha/include/asm/spinlock.h | 9 +++++++--
arch/arc/include/asm/spinlock.h | 7 +++++--
arch/arm/include/asm/spinlock.h | 19 +++++++++++++++++--
arch/blackfin/include/asm/spinlock.h | 5 +++--
arch/hexagon/include/asm/spinlock.h | 10 ++++++++--
arch/ia64/include/asm/spinlock.h | 4 ++++
arch/m32r/include/asm/spinlock.h | 9 +++++++--
arch/metag/include/asm/spinlock.h | 14 ++++++++++++--
arch/mips/include/asm/spinlock.h | 19 +++++++++++++++++--
arch/mn10300/include/asm/spinlock.h | 8 +++++++-
arch/parisc/include/asm/spinlock.h | 9 +++++++--
arch/powerpc/include/asm/spinlock.h | 8 ++++++--
arch/s390/include/asm/spinlock.h | 3 +++
arch/sh/include/asm/spinlock.h | 10 ++++++++--
arch/sparc/include/asm/spinlock_32.h | 7 +++++--
arch/sparc/include/asm/spinlock_64.h | 10 +++++++---
arch/tile/lib/spinlock_32.c | 6 ++++++
arch/tile/lib/spinlock_64.c | 6 ++++++
arch/xtensa/include/asm/spinlock.h | 10 ++++++++--
include/asm-generic/barrier.h | 2 +-
include/asm-generic/qspinlock.h | 5 +++--
include/linux/spinlock_up.h | 10 +++++++---
22 files changed, 154 insertions(+), 36 deletions(-)
--- a/arch/alpha/include/asm/spinlock.h
+++ b/arch/alpha/include/asm/spinlock.h
@@ -3,6 +3,8 @@
#include <linux/kernel.h>
#include <asm/current.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
/*
* Simple spin lock operations. There are two variants, one clears IRQ's
@@ -13,8 +15,11 @@
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
#define arch_spin_is_locked(x) ((x)->lock != 0)
-#define arch_spin_unlock_wait(x) \
- do { cpu_relax(); } while ((x)->lock)
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, !VAL);
+}
static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
--- a/arch/arc/include/asm/spinlock.h
+++ b/arch/arc/include/asm/spinlock.h
@@ -15,8 +15,11 @@
#define arch_spin_is_locked(x) ((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-#define arch_spin_unlock_wait(x) \
- do { while (arch_spin_is_locked(x)) cpu_relax(); } while (0)
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, !VAL);
+}
#ifdef CONFIG_ARC_HAS_LLSC
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -6,6 +6,8 @@
#endif
#include <linux/prefetch.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
/*
* sev and wfe are ARMv6K extensions. Uniprocessor ARMv6 may not have the K
@@ -50,8 +52,21 @@ static inline void dsb_sev(void)
* memory.
*/
-#define arch_spin_unlock_wait(lock) \
- do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ u16 owner = READ_ONCE(lock->tickets.owner);
+
+ for (;;) {
+ arch_spinlock_t tmp = READ_ONCE(*lock);
+
+ if (tmp.tickets.owner == tmp.tickets.next ||
+ tmp.tickets.owner != owner)
+ break;
+
+ wfe();
+ }
+ smp_acquire__after_ctrl_dep();
+}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
--- a/arch/blackfin/include/asm/spinlock.h
+++ b/arch/blackfin/include/asm/spinlock.h
@@ -12,6 +12,8 @@
#else
#include <linux/atomic.h>
+#include <asm/processor.h>
+#include <asm/barrier.h>
asmlinkage int __raw_spin_is_locked_asm(volatile int *ptr);
asmlinkage void __raw_spin_lock_asm(volatile int *ptr);
@@ -48,8 +50,7 @@ static inline void arch_spin_unlock(arch
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
- while (arch_spin_is_locked(lock))
- cpu_relax();
+ smp_cond_load_acquire(&lock->lock, !VAL);
}
static inline int arch_read_can_lock(arch_rwlock_t *rw)
--- a/arch/hexagon/include/asm/spinlock.h
+++ b/arch/hexagon/include/asm/spinlock.h
@@ -23,6 +23,8 @@
#define _ASM_SPINLOCK_H
#include <asm/irqflags.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
/*
* This file is pulled in for SMP builds.
@@ -176,8 +178,12 @@ static inline unsigned int arch_spin_try
* SMP spinlocks are intended to allow only a single CPU at the lock
*/
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-#define arch_spin_unlock_wait(lock) \
- do {while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, !VAL);
+}
+
#define arch_spin_is_locked(x) ((x)->lock != 0)
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
--- a/arch/ia64/include/asm/spinlock.h
+++ b/arch/ia64/include/asm/spinlock.h
@@ -15,6 +15,8 @@
#include <linux/atomic.h>
#include <asm/intrinsics.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
#define arch_spin_lock_init(x) ((x)->lock = 0)
@@ -86,6 +88,8 @@ static __always_inline void __ticket_spi
return;
cpu_relax();
}
+
+ smp_acquire__after_ctrl_dep();
}
static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
--- a/arch/m32r/include/asm/spinlock.h
+++ b/arch/m32r/include/asm/spinlock.h
@@ -13,6 +13,8 @@
#include <linux/atomic.h>
#include <asm/dcache_clear.h>
#include <asm/page.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
@@ -27,8 +29,11 @@
#define arch_spin_is_locked(x) (*(volatile int *)(&(x)->slock) <= 0)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-#define arch_spin_unlock_wait(x) \
- do { cpu_relax(); } while (arch_spin_is_locked(x))
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, VAL > 0);
+}
/**
* arch_spin_trylock - Try spin lock and return a result
--- a/arch/metag/include/asm/spinlock.h
+++ b/arch/metag/include/asm/spinlock.h
@@ -1,14 +1,24 @@
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
#ifdef CONFIG_METAG_ATOMICITY_LOCK1
#include <asm/spinlock_lock1.h>
#else
#include <asm/spinlock_lnkget.h>
#endif
-#define arch_spin_unlock_wait(lock) \
- do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+/*
+ * both lock1 and lnkget are test-and-set spinlocks with 0 unlocked and 1
+ * locked.
+ */
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, !VAL);
+}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
--- a/arch/mips/include/asm/spinlock.h
+++ b/arch/mips/include/asm/spinlock.h
@@ -12,6 +12,7 @@
#include <linux/compiler.h>
#include <asm/barrier.h>
+#include <asm/processor.h>
#include <asm/compiler.h>
#include <asm/war.h>
@@ -48,8 +49,22 @@ static inline int arch_spin_value_unlock
}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-#define arch_spin_unlock_wait(x) \
- while (arch_spin_is_locked(x)) { cpu_relax(); }
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ u16 owner = READ_ONCE(lock->h.serving_now);
+ smp_rmb();
+ for (;;) {
+ arch_spinlock_t tmp = READ_ONCE(*lock);
+
+ if (tmp.h.serving_now == tmp.h.ticket ||
+ tmp.h.serving_now != owner)
+ break;
+
+ cpu_relax();
+ }
+ smp_acquire__after_ctrl_dep();
+}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
--- a/arch/mn10300/include/asm/spinlock.h
+++ b/arch/mn10300/include/asm/spinlock.h
@@ -12,6 +12,8 @@
#define _ASM_SPINLOCK_H
#include <linux/atomic.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
#include <asm/rwlock.h>
#include <asm/page.h>
@@ -23,7 +25,11 @@
*/
#define arch_spin_is_locked(x) (*(volatile signed char *)(&(x)->slock) != 0)
-#define arch_spin_unlock_wait(x) do { barrier(); } while (arch_spin_is_locked(x))
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, !VAL);
+}
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
--- a/arch/parisc/include/asm/spinlock.h
+++ b/arch/parisc/include/asm/spinlock.h
@@ -13,8 +13,13 @@ static inline int arch_spin_is_locked(ar
}
#define arch_spin_lock(lock) arch_spin_lock_flags(lock, 0)
-#define arch_spin_unlock_wait(x) \
- do { cpu_relax(); } while (arch_spin_is_locked(x))
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *x)
+{
+ volatile unsigned int *a = __ldcw_align(x);
+
+ smp_cond_load_acquire(a, VAL);
+}
static inline void arch_spin_lock_flags(arch_spinlock_t *x,
unsigned long flags)
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -27,6 +27,8 @@
#include <asm/asm-compat.h>
#include <asm/synch.h>
#include <asm/ppc-opcode.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
#ifdef CONFIG_PPC64
/* use 0x800000yy when locked, where yy == CPU number */
@@ -165,8 +167,10 @@ static inline void arch_spin_unlock(arch
#ifdef CONFIG_PPC64
extern void arch_spin_unlock_wait(arch_spinlock_t *lock);
#else
-#define arch_spin_unlock_wait(lock) \
- do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, !VAL);
+}
#endif
/*
--- a/arch/s390/include/asm/spinlock.h
+++ b/arch/s390/include/asm/spinlock.h
@@ -10,6 +10,8 @@
#define __ASM_SPINLOCK_H
#include <linux/smp.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
#define SPINLOCK_LOCKVAL (S390_lowcore.spinlock_lockval)
@@ -97,6 +99,7 @@ static inline void arch_spin_unlock_wait
{
while (arch_spin_is_locked(lock))
arch_spin_relax(lock);
+ smp_acquire__after_ctrl_dep();
}
/*
--- a/arch/sh/include/asm/spinlock.h
+++ b/arch/sh/include/asm/spinlock.h
@@ -19,14 +19,20 @@
#error "Need movli.l/movco.l for spinlocks"
#endif
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
*/
#define arch_spin_is_locked(x) ((x)->lock <= 0)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-#define arch_spin_unlock_wait(x) \
- do { while (arch_spin_is_locked(x)) cpu_relax(); } while (0)
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, VAL > 0);
+}
/*
* Simple spin lock operations. There are two variants, one clears IRQ's
--- a/arch/sparc/include/asm/spinlock_32.h
+++ b/arch/sparc/include/asm/spinlock_32.h
@@ -9,12 +9,15 @@
#ifndef __ASSEMBLY__
#include <asm/psr.h>
+#include <asm/barrier.h>
#include <asm/processor.h> /* for cpu_relax */
#define arch_spin_is_locked(lock) (*((volatile unsigned char *)(lock)) != 0)
-#define arch_spin_unlock_wait(lock) \
- do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, !VAL);
+}
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
--- a/arch/sparc/include/asm/spinlock_64.h
+++ b/arch/sparc/include/asm/spinlock_64.h
@@ -8,6 +8,9 @@
#ifndef __ASSEMBLY__
+#include <asm/processor.h>
+#include <asm/barrier.h>
+
/* To get debugging spinlocks which detect and catch
* deadlock situations, set CONFIG_DEBUG_SPINLOCK
* and rebuild your kernel.
@@ -23,9 +26,10 @@
#define arch_spin_is_locked(lp) ((lp)->lock != 0)
-#define arch_spin_unlock_wait(lp) \
- do { rmb(); \
- } while((lp)->lock)
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->lock, !VAL);
+}
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
--- a/arch/tile/lib/spinlock_32.c
+++ b/arch/tile/lib/spinlock_32.c
@@ -76,6 +76,12 @@ void arch_spin_unlock_wait(arch_spinlock
do {
delay_backoff(iterations++);
} while (READ_ONCE(lock->current_ticket) == curr);
+
+ /*
+ * The TILE architecture doesn't do read speculation; therefore
+ * a control dependency guarantees a LOAD->{LOAD,STORE} order.
+ */
+ barrier();
}
EXPORT_SYMBOL(arch_spin_unlock_wait);
--- a/arch/tile/lib/spinlock_64.c
+++ b/arch/tile/lib/spinlock_64.c
@@ -76,6 +76,12 @@ void arch_spin_unlock_wait(arch_spinlock
do {
delay_backoff(iterations++);
} while (arch_spin_current(READ_ONCE(lock->lock)) == curr);
+
+ /*
+ * The TILE architecture doesn't do read speculation; therefore
+ * a control dependency guarantees a LOAD->{LOAD,STORE} order.
+ */
+ barrier();
}
EXPORT_SYMBOL(arch_spin_unlock_wait);
--- a/arch/xtensa/include/asm/spinlock.h
+++ b/arch/xtensa/include/asm/spinlock.h
@@ -11,6 +11,9 @@
#ifndef _XTENSA_SPINLOCK_H
#define _XTENSA_SPINLOCK_H
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
/*
* spinlock
*
@@ -29,8 +32,11 @@
*/
#define arch_spin_is_locked(x) ((x)->slock != 0)
-#define arch_spin_unlock_wait(lock) \
- do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
+
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, !VAL);
+}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -194,7 +194,7 @@ do { \
})
#endif
-#endif
+#endif /* CONFIG_SMP */
/* Barriers for virtual machine guests when talking to an SMP host */
#define virt_mb() __smp_mb()
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -20,6 +20,8 @@
#define __ASM_GENERIC_QSPINLOCK_H
#include <asm-generic/qspinlock_types.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
/**
* queued_spin_is_locked - is the spinlock locked?
@@ -133,8 +135,7 @@ static inline void queued_spin_unlock_wa
{
/* See queued_spin_is_locked() */
smp_mb();
- while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
- cpu_relax();
+ smp_cond_load_acquire(&lock->val.counter, !(VAL & _Q_LOCKED_MASK));
}
#ifndef virt_spin_lock
--- a/include/linux/spinlock_up.h
+++ b/include/linux/spinlock_up.h
@@ -6,6 +6,7 @@
#endif
#include <asm/processor.h> /* for cpu_relax() */
+#include <asm/barrier.h>
/*
* include/linux/spinlock_up.h - UP-debug version of spinlocks.
@@ -25,6 +26,11 @@
#ifdef CONFIG_DEBUG_SPINLOCK
#define arch_spin_is_locked(x) ((x)->slock == 0)
+static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
+{
+ smp_cond_load_acquire(&lock->slock, VAL);
+}
+
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
lock->slock = 0;
@@ -67,6 +73,7 @@ static inline void arch_spin_unlock(arch
#else /* DEBUG_SPINLOCK */
#define arch_spin_is_locked(lock) ((void)(lock), 0)
+#define arch_spin_unlock_wait(lock) do { barrier(); (void)(lock); } while (0)
/* for sched/core.c and kernel_lock.c: */
# define arch_spin_lock(lock) do { barrier(); (void)(lock); } while (0)
# define arch_spin_lock_flags(lock, flags) do { barrier(); (void)(lock); } while (0)
@@ -79,7 +86,4 @@ static inline void arch_spin_unlock(arch
#define arch_read_can_lock(lock) (((void)(lock), 1))
#define arch_write_can_lock(lock) (((void)(lock), 1))
-#define arch_spin_unlock_wait(lock) \
- do { cpu_relax(); } while (arch_spin_is_locked(lock))
-
#endif /* __LINUX_SPINLOCK_UP_H */