[PATCH -v2 4/6] locking, arch: Update spin_unlock_wait()

Peter Zijlstra
2016-05-26T14:28:08Z

[-- Attachment #1: peterz-locking-spin_unlock_wait.patch --]
[-- Type: text/plain, Size: 13354 bytes --]

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: rth@twiddle.net
Cc: vgupta@synopsys.com
Cc: linux@armlinux.org.uk
Cc: realmz6@gmail.com
Cc: rkuo@codeaurora.org
Cc: tony.luck@intel.com
Cc: james.hogan@imgtec.com
Cc: ralf@linux-mips.org
Cc: dhowells@redhat.com
Cc: jejb@parisc-linux.org
Cc: mpe@ellerman.id.au
Cc: schwidefsky@de.ibm.com
Cc: ysato@users.sourceforge.jp
Cc: davem@davemloft.net
Cc: cmetcalf@mellanox.com
Cc: chris@zankel.net
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/alpha/include/asm/spinlock.h | 7 +++++--
arch/arc/include/asm/spinlock.h | 7 +++++--
arch/arm/include/asm/spinlock.h | 18 ++++++++++++++++--
arch/blackfin/include/asm/spinlock.h | 3 +--
arch/hexagon/include/asm/spinlock.h | 8 ++++++--
arch/ia64/include/asm/spinlock.h | 2 ++
arch/m32r/include/asm/spinlock.h | 7 +++++--
arch/metag/include/asm/spinlock.h | 11 +++++++++--
arch/mips/include/asm/spinlock.h | 18 ++++++++++++++++--
arch/mn10300/include/asm/spinlock.h | 6 +++++-
arch/parisc/include/asm/spinlock.h | 9 +++++++--
arch/powerpc/include/asm/spinlock.h | 6 ++++--
arch/s390/include/asm/spinlock.h | 3 +--
arch/sh/include/asm/spinlock.h | 7 +++++--
arch/sparc/include/asm/spinlock_32.h | 6 ++++--
arch/sparc/include/asm/spinlock_64.h | 9 ++++++---
arch/tile/lib/spinlock_32.c | 4 ++++
arch/tile/lib/spinlock_64.c | 4 ++++
arch/xtensa/include/asm/spinlock.h | 7 +++++--
include/asm-generic/qspinlock.h | 3 +--
include/linux/spinlock_up.h | 9 ++++++---
21 files changed, 117 insertions(+), 37 deletions(-)

--- a/arch/alpha/include/asm/spinlock.h
+++ b/arch/alpha/include/asm/spinlock.h
@@ -13,8 +13,11 @@

#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
@@ -50,8 +50,22 @@ 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);
+
+ smp_rmb();
+ 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
@@ -48,8 +48,7 @@ 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
@@ -176,8 +176,12 @@ 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
@@ -86,6 +86,8 @@ 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
@@ -27,8 +27,11 @@

#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
@@ -7,8 +7,15 @@
#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
@@ -48,8 +48,22 @@ 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
@@ -23,7 +23,11 @@
*/

#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
@@ -165,8 +165,10 @@ 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
@@ -95,8 +95,7 @@ static inline void arch_spin_unlock(arch

static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
- while (arch_spin_is_locked(lock))
- arch_spin_relax(lock);
+ smp_cond_load_acquire(&lock->lock, !VAL);
}

/*
--- a/arch/sh/include/asm/spinlock.h
+++ b/arch/sh/include/asm/spinlock.h
@@ -25,8 +25,11 @@

#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
@@ -13,8 +13,10 @@

#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 +8,8 @@

#ifndef __ASSEMBLY__

+#include <asm/process.h>
+
/* To get debugging spinlocks which detect and catch
* deadlock situations, set CONFIG_DEBUG_SPINLOCK
* and rebuild your kernel.
@@ -23,9 +25,10 @@

#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
@@ -72,10 +72,14 @@ void arch_spin_unlock_wait(arch_spinlock
if (next == curr)
return;

+ smp_rmb();
+
/* Wait until the current locker has released the lock. */
do {
delay_backoff(iterations++);
} while (READ_ONCE(lock->current_ticket) == curr);
+
+ smp_acquire__after_ctrl_dep();
}
EXPORT_SYMBOL(arch_spin_unlock_wait);

--- a/arch/tile/lib/spinlock_64.c
+++ b/arch/tile/lib/spinlock_64.c
@@ -72,10 +72,14 @@ void arch_spin_unlock_wait(arch_spinlock
if (arch_spin_next(val) == curr)
return;

+ smp_rmb();
+
/* Wait until the current locker has released the lock. */
do {
delay_backoff(iterations++);
} while (arch_spin_current(READ_ONCE(lock->lock)) == curr);
+
+ smp_acquire__after_ctrl_dep();
}
EXPORT_SYMBOL(arch_spin_unlock_wait);

--- a/arch/xtensa/include/asm/spinlock.h
+++ b/arch/xtensa/include/asm/spinlock.h
@@ -29,8 +29,11 @@
*/

#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/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -133,8 +133,7 @@ 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
@@ -25,6 +25,11 @@
#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 +72,7 @@ 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 +85,4 @@ 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 */