From cee4393989333795ae04dc9f3b83a578afe3fca6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 2 Mar 2018 16:35:27 -0800 Subject: rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() Commit e31d28b6ab8f ("trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched()") substituted cond_resched() for the earlier call to cond_resched_rcu_qs(). However, the new-age cond_resched() does not do anything to help RCU-tasks grace periods because (1) RCU-tasks is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a complete no-op when preemption is enabled. This situation results in hangs when running the trace benchmarks. A number of potential fixes were discussed on LKML (https://lkml.kernel.org/r/20180224151240.0d63a059@vmware.local.home), including making cond_resched() not be a no-op; making cond_resched() not be a no-op, but only when running tracing benchmarks; reverting the aforementioned commit (which works because cond_resched_rcu_qs() does provide an RCU-tasks quiescent state; and adding a call to the scheduler/RCU rcu_note_voluntary_context_switch() function. All were deemed unsatisfactory, either due to added cond_resched() overhead or due to magic functions inviting cargo culting. This commit renames cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs(), which provides a clear hint as to what this function is doing and why and where it should be used, and then replaces the call to cond_resched() with cond_resched_tasks_rcu_qs() in the trace benchmark's benchmark_event_kthread() function. Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Tested-by: Nicholas Piggin --- kernel/torture.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/torture.c') diff --git a/kernel/torture.c b/kernel/torture.c index 37b94012a3f8..3de1efbecd6a 100644 --- a/kernel/torture.c +++ b/kernel/torture.c @@ -574,7 +574,7 @@ void stutter_wait(const char *title) { int spt; - cond_resched_rcu_qs(); + cond_resched_tasks_rcu_qs(); spt = READ_ONCE(stutter_pause_test); for (; spt; spt = READ_ONCE(stutter_pause_test)) { if (spt == 1) { -- cgit v1.2.3-59-g8ed1b