diff options
| -rw-r--r-- | arch/arm64/include/asm/spinlock.h | 9 | ||||
| -rw-r--r-- | kernel/locking/osq_lock.c | 23 |
2 files changed, 19 insertions, 13 deletions
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index b093b287babf..102404dc1e13 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -11,4 +11,13 @@ /* See include/linux/spinlock.h */ #define smp_mb__after_spinlock() smp_mb() +/* + * Changing this will break osq_lock() thanks to the call inside + * smp_cond_load_relaxed(). + * + * See: + * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net + */ +#define vcpu_is_preempted(cpu) false + #endif /* __ASM_SPINLOCK_H */ diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 6ef600aa0f47..1f7734949ac8 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -134,20 +134,17 @@ bool osq_lock(struct optimistic_spin_queue *lock) * cmpxchg in an attempt to undo our queueing. */ - while (!READ_ONCE(node->locked)) { - /* - * If we need to reschedule bail... so we can block. - * Use vcpu_is_preempted() to avoid waiting for a preempted - * lock holder: - */ - if (need_resched() || vcpu_is_preempted(node_cpu(node->prev))) - goto unqueue; - - cpu_relax(); - } - return true; + /* + * Wait to acquire the lock or cancelation. Note that need_resched() + * will come with an IPI, which will wake smp_cond_load_relaxed() if it + * is implemented with a monitor-wait. vcpu_is_preempted() relies on + * polling, be careful. + */ + if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() || + vcpu_is_preempted(node_cpu(node->prev)))) + return true; -unqueue: + /* unqueue */ /* * Step - A -- stabilize @prev * |