From: "Paul E. McKenney" paulmck@linux.vnet.ibm.com
[ Upstream commit 68ab0b4263224157f4d0c0e42854169a183d7534 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- kernel/rcu/update.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 4f6db7e6a117..2164c9cc6fd8 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -346,6 +346,7 @@ 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++) { @@ -357,7 +358,11 @@ 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. */ @@ -366,7 +371,11 @@ 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); } }