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Commit 68ab0b42 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make synchronize_rcu_mult() check for duplicates 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent a602538e

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);

	}