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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-04-28 16:19:07 -07:00
parent a602538e46
commit 68ab0b4263
1 changed files with 11 additions and 2 deletions
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9
kernel/rcu/update.c
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@ -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);
}