The following commit has been merged into the sched/core branch of tip:
Commit-ID: 3a7b5c87a0b29c8554a9bdbbbd75eeb4176fb5d4 Gitweb: https://git.kernel.org/tip/3a7b5c87a0b29c8554a9bdbbbd75eeb4176fb5d4 Author: Frederic Weisbecker frederic@kernel.org AuthorDate: Mon, 01 Feb 2021 00:05:45 +01:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Wed, 10 Feb 2021 14:44:50 +01:00
rcu/nocb: Perform deferred wake up before last idle's need_resched() check
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 Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-3-frederic@kernel.org --- 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(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index fd02c5f..36c2119 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -110,8 +110,10 @@ 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 */
/** diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 63032e5..82838e9 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -671,10 +671,7 @@ static noinstr 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); } EXPORT_SYMBOL_GPL(rcu_idle_enter); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7e291ce..d5b38c2 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2187,6 +2187,11 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 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; diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 305727e..7199e6f 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -285,6 +285,7 @@ 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