Merge branch 'core-rcu.2021.08.28a' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-2.6-microblaze.git] / kernel / sched / core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f3b27c6..2b9ed11 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7849,6 +7849,17 @@ int __sched __cond_resched(void)
                preempt_schedule_common();
                return 1;
        }
+       /*
+        * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
+        * whether the current CPU is in an RCU read-side critical section,
+        * so the tick can report quiescent states even for CPUs looping
+        * in kernel context.  In contrast, in non-preemptible kernels,
+        * RCU readers leave no in-memory hints, which means that CPU-bound
+        * processes executing in kernel context might never report an
+        * RCU quiescent state.  Therefore, the following code causes
+        * cond_resched() to report a quiescent state, but only when RCU
+        * is in urgent need of one.
+        */
 #ifndef CONFIG_PREEMPT_RCU
        rcu_all_qs();
 #endif