diff options
| -rw-r--r-- | arch/arm64/include/asm/spinlock.h | 9 | ||||
| -rw-r--r-- | kernel/locking/lockdep_proc.c | 4 | ||||
| -rw-r--r-- | kernel/locking/osq_lock.c | 23 | ||||
| -rw-r--r-- | kernel/locking/qspinlock.c | 13 |
4 files changed, 28 insertions, 21 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/lockdep_proc.c b/kernel/locking/lockdep_proc.c index dadb7b7fba37..9bb6d2497b04 100644 --- a/kernel/locking/lockdep_proc.c +++ b/kernel/locking/lockdep_proc.c @@ -286,9 +286,9 @@ static int lockdep_stats_show(struct seq_file *m, void *v) seq_printf(m, " stack-trace entries: %11lu [max: %lu]\n", nr_stack_trace_entries, MAX_STACK_TRACE_ENTRIES); #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) - seq_printf(m, " number of stack traces: %llu\n", + seq_printf(m, " number of stack traces: %11llu\n", lockdep_stack_trace_count()); - seq_printf(m, " number of stack hash chains: %llu\n", + seq_printf(m, " number of stack hash chains: %11llu\n", lockdep_stack_hash_count()); #endif seq_printf(m, " combined max dependencies: %11u\n", 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 * diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 2473f10c6956..b9515fcc9b29 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -31,14 +31,15 @@ /* * The basic principle of a queue-based spinlock can best be understood * by studying a classic queue-based spinlock implementation called the - * MCS lock. The paper below provides a good description for this kind - * of lock. + * MCS lock. A copy of the original MCS lock paper ("Algorithms for Scalable + * Synchronization on Shared-Memory Multiprocessors by Mellor-Crummey and + * Scott") is available at * - * http://www.cise.ufl.edu/tr/DOC/REP-1992-71.pdf + * https://bugzilla.kernel.org/show_bug.cgi?id=206115 * - * This queued spinlock implementation is based on the MCS lock, however to make - * it fit the 4 bytes we assume spinlock_t to be, and preserve its existing - * API, we must modify it somehow. + * This queued spinlock implementation is based on the MCS lock, however to + * make it fit the 4 bytes we assume spinlock_t to be, and preserve its + * existing API, we must modify it somehow. * * In particular; where the traditional MCS lock consists of a tail pointer * (8 bytes) and needs the next pointer (another 8 bytes) of its own node to |