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locking/spinlock, arch: Update and fix spin_unlock_wait() implementations

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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.

Note: PPC32 will be fixed independently

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2016-05-26 10:35:03 +02:00 • committed by Ingo Molnar
commit 726328d92a
20 changed files with 145 additions and 32 deletions
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10
arch/xtensa/include/asm/spinlock.h
View file

@ -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)