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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-03-03 03:35:27 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-05-15 20:27:29 +0300
commitcee4393989333795ae04dc9f3b83a578afe3fca6 (patch)
tree9b3afa8f132956c603f83a1fb098f8d30a81d7c1 /kernel/rcu/update.c
parent6fba2b3767ea6e3e1204855031492415cc4dce4f (diff)
downloadlinux-cee4393989333795ae04dc9f3b83a578afe3fca6.tar.xz
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 <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Nicholas Piggin <npiggin@gmail.com>
Diffstat (limited to 'kernel/rcu/update.c')
-rw-r--r--kernel/rcu/update.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 68fa19a5e7bd..e401960c7f51 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -624,7 +624,7 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks);
* grace period has elapsed, in other words after all currently
* executing rcu-tasks read-side critical sections have elapsed. These
* read-side critical sections are delimited by calls to schedule(),
- * cond_resched_rcu_qs(), idle execution, userspace execution, calls
+ * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
*
* This is a very specialized primitive, intended only for a few uses in