From 68ab0b4263224157f4d0c0e42854169a183d7534 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 28 Apr 2017 16:19:07 -0700 Subject: 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 --- kernel/rcu/update.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'kernel/rcu') diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 82a5aa10dbc5..123a9c4b5055 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -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++) { @@ -390,7 +391,11 @@ 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); - (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu); + 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); } /* Wait for all callbacks to be invoked. */ @@ -399,7 +404,11 @@ 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; - wait_for_completion(&rs_array[i].completion); + 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); } } -- cgit v1.2.3