[tip: core/rcu] rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     cf868c2af244417ed276ba7f716b980841a71340
Gitweb:        https://git.kernel.org/tip/cf868c2af244417ed276ba7f716b980841a71340
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Wed, 24 Mar 2021 17:08:48 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Tue, 18 May 2021 10:54:51 -07:00

rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states

Heavy networking load can cause a CPU to execute continuously and
indefinitely within ksoftirqd, in which case there will be no voluntary
task switches and thus no RCU-tasks quiescent states.  This commit
therefore causes the exiting rcu_softirq_qs() to provide an RCU-tasks
quiescent state.

This of course means that __do_softirq() and its callers cannot be
invoked from within a tracing trampoline.

Reported-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Tested-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8e78b24..f4daa4e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -242,6 +242,7 @@ void rcu_softirq_qs(void)
 {
 	rcu_qs();
 	rcu_preempt_deferred_qs(current);
+	rcu_tasks_qs(current, false);
 }
 
 /*