From 43789ef3f7d61aa7bed0cb2764e588fc990c30ef Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@kernel.org>
Date: Mon, 1 Feb 2021 00:05:45 +0100
Subject: [PATCH] rcu/nocb: Perform deferred wake up before last idle's
need_resched() check
Git-commit: 43789ef3f7d61aa7bed0cb2764e588fc990c30ef
Patch-mainline: v5.12-rc1
References: git-fixes
Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
kthread (rcuog) to be serviced.
Usually a local wake up happening while running the idle task is handled
in one of the need_resched() checks carefully placed within the idle
loop that can break to the scheduler.
Unfortunately the call to rcu_idle_enter() is already beyond the last
generic need_resched() check and we may halt the CPU with a resched
request unhandled, leaving the task hanging.
Fix this with splitting the rcuog wakeup handling from rcu_idle_enter()
and place it before the last generic need_resched() check in the idle
loop. It is then assumed that no call to call_rcu() will be performed
after that in the idle loop until the CPU is put in low power mode.
Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf)
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-3-frederic@kernel.org
Signed-off-by: Frederic Weisbecker <fweisbecker@suse.com>
---
include/linux/rcupdate.h | 2 ++
kernel/rcu/tree.c | 3 ---
kernel/rcu/tree_plugin.h | 5 +++++
kernel/sched/idle.c | 1 +
4 files changed, 8 insertions(+), 3 deletions(-)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -96,8 +96,10 @@ static inline void rcu_user_exit(void) {
#ifdef CONFIG_RCU_NOCB_CPU
void rcu_init_nohz(void);
+void rcu_nocb_flush_deferred_wakeup(void);
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static inline void rcu_init_nohz(void) { }
+static inline void rcu_nocb_flush_deferred_wakeup(void) { }
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
/**
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -592,10 +592,7 @@ static void rcu_eqs_enter(bool user)
*/
void rcu_idle_enter(void)
{
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
-
lockdep_assert_irqs_disabled();
- do_nocb_deferred_wakeup(rdp);
rcu_eqs_enter(false);
}
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2020,6 +2020,11 @@ static void do_nocb_deferred_wakeup(stru
do_nocb_deferred_wakeup_common(rdp);
}
+void rcu_nocb_flush_deferred_wakeup(void)
+{
+ do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
+}
+
void __init rcu_init_nohz(void)
{
int cpu;
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -250,6 +250,7 @@ static void do_idle(void)
}
arch_cpu_idle_enter();
+ rcu_nocb_flush_deferred_wakeup();
/*
* In poll mode we reenable interrupts and spin. Also if we