rcu: Make synchronize_rcu_mult() check for duplicates (68ab0b42) · Commits · 戴 / test

Currently, doing synchronize_rcu_mult(call_rcu, call_rcu) might (or might not) wait for two RCU grace periods. One approach is of course "don't do that!", but in CONFIG_PREEMPT=n kernels, synchronize_rcu_mult(call_rcu, call_rcu_sched) does exactly that. This results in an ugly #ifdef in sched_cpu_deactivate(). This commit therefore makes __wait_rcu_gp() check for duplicates, which in turn allows duplicates to be passed to synchronize_rcu_mult() without risk of waiting twice on the same type of grace period. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/update.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -379,6 +379,7 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
		struct rcu_synchronize *rs_array)
		{
		int i;
		int j;

		/* Initialize and register callbacks for each flavor specified. */
		for (i = 0; i < n; i++) {
		@@ -390,6 +391,10 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
		}
		init_rcu_head_on_stack(&rs_array[i].head);
		init_completion(&rs_array[i].completion);
		for (j = 0; j < i; j++)
		if (crcu_array[j] == crcu_array[i])
		break;
		if (j == i)
		(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
		}

		@@ -399,6 +404,10 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
		(crcu_array[i] == call_rcu \|\|
		crcu_array[i] == call_rcu_bh))
		continue;
		for (j = 0; j < i; j++)
		if (crcu_array[j] == crcu_array[i])
		break;
		if (j == i)
		wait_for_completion(&rs_array[i].completion);
		destroy_rcu_head_on_stack(&rs_array[i].head);
		}

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