@@ -1684,21 +1684,11 @@ static void rcu_sr_normal_gp_cleanup(void)
WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail));
/*
- * Process (a) and (d) cases. See an illustration. Apart of
- * that it handles the scenario when all clients are done,
- * wait-head is released if last. The worker is not kicked.
+ * Process (a) and (d) cases. See an illustration.
*/
llist_for_each_safe(rcu, next, wait_tail->next) {
- if (rcu_sr_is_wait_head(rcu)) {
- if (!rcu->next) {
- rcu_sr_put_wait_head(rcu);
- wait_tail->next = NULL;
- } else {
- wait_tail->next = rcu;
- }
-
+ if (rcu_sr_is_wait_head(rcu))
break;
- }
rcu_sr_normal_complete(rcu);
// It can be last, update a next on this step.
@@ -1712,8 +1702,12 @@ static void rcu_sr_normal_gp_cleanup(void)
smp_store_release(&rcu_state.srs_done_tail, wait_tail);
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail);
- if (wait_tail->next)
- schedule_work(&rcu_state.srs_cleanup_work);
+ /*
+ * We schedule a work in order to perform a final processing
+ * of outstanding users(if still left) and releasing wait-heads
+ * added by rcu_sr_normal_gp_init() call.
+ */
+ schedule_work(&rcu_state.srs_cleanup_work);
}
/*
Fix a below race by not releasing a wait-head from the GP-kthread as it can lead for reusing it whereas a worker can still access it thus execute newly added callbacks too early. CPU 0 CPU 1 ----- ----- // wait_tail == HEAD1 rcu_sr_normal_gp_cleanup() { // has passed SR_MAX_USERS_WAKE_FROM_GP wait_tail->next = next; // done_tail = HEAD1 smp_store_release(&rcu_state.srs_done_tail, wait_tail); queue_work() { test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work) __queue_work() } } set_work_pool_and_clear_pending() rcu_sr_normal_gp_cleanup_work() { // new GP, wait_tail == HEAD2 rcu_sr_normal_gp_cleanup() { // executes all completion, but stop at HEAD1 wait_tail->next = HEAD1; // done_tail = HEAD2 smp_store_release(&rcu_state.srs_done_tail, wait_tail); queue_work() { test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work) __queue_work() } } // done = HEAD2 done = smp_load_acquire(&rcu_state.srs_done_tail); // head = HEAD1 head = done->next; done->next = NULL; llist_for_each_safe() { // completes all callbacks, release HEAD1 } } // Process second queue set_work_pool_and_clear_pending() rcu_sr_normal_gp_cleanup_work() { // done = HEAD2 done = smp_load_acquire(&rcu_state.srs_done_tail); // new GP, wait_tail == HEAD3 rcu_sr_normal_gp_cleanup() { // Finds HEAD2 with ->next == NULL at the end rcu_sr_put_wait_head(HEAD2) ... // A few more GPs later rcu_sr_normal_gp_init() { HEAD2 = rcu_sr_get_wait_head(); llist_add(HEAD2, &rcu_state.srs_next); // head == rcu_state.srs_next head = done->next; done->next = NULL; llist_for_each_safe() { // EXECUTE CALLBACKS TOO EARLY!!! } } Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Reported-by: Frederic Weisbecker <frederic@kernel.org> Fixes: 05a10b921000 ("rcu: Support direct wake-up of synchronize_rcu() users") Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> --- kernel/rcu/tree.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-)