change system file

hc

2024-10-09 244b2c5ca8b14627e4a17755e5922221e121c771

 kernel/kernel/locking/osq_lock.c
..
..
@@ -134,20 +134,17 @@
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 	 * cmpxchg in an attempt to undo our queueing.
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 	 */
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-	while (!READ_ONCE(node->locked)) {
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-		/*
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-		 * If we need to reschedule bail... so we can block.
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-		 * Use vcpu_is_preempted() to avoid waiting for a preempted
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-		 * lock holder:
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-		 */
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-		if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
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-			goto unqueue;
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+	/*
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+	 * Wait to acquire the lock or cancelation. Note that need_resched()
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+	 * will come with an IPI, which will wake smp_cond_load_relaxed() if it
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+	 * is implemented with a monitor-wait. vcpu_is_preempted() relies on
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+	 * polling, be careful.
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+	 */
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+	if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() ||
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+				  vcpu_is_preempted(node_cpu(node->prev))))
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+		return true;
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-		cpu_relax();
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-	}
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-	return true;
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-
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-unqueue:
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+	/* unqueue */
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 	/*
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 	 * Step - A  -- stabilize @prev
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 	 *
..
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@@ -157,7 +154,11 @@
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 	 */
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 	for (;;) {
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-		if (prev->next == node &&
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+		/*
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+		 * cpu_relax() below implies a compiler barrier which would
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+		 * prevent this comparison being optimized away.
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+		 */
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+		if (data_race(prev->next) == node &&
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 		    cmpxchg(&prev->next, node, NULL) == node)
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 			break;
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