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authorFrederic Weisbecker <frederic@kernel.org>2021-02-01 00:05:45 +0100
committerIngo Molnar <mingo@kernel.org>2021-02-17 14:12:43 +0100
commit43789ef3f7d61aa7bed0cb2764e588fc990c30ef (patch)
tree016b9a4436405a6e74d362ec2739ab20a578ccf7 /kernel/rcu
parentrcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers (diff)
downloadlinux-43789ef3f7d61aa7bed0cb2764e588fc990c30ef.tar.xz
linux-43789ef3f7d61aa7bed0cb2764e588fc990c30ef.zip
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> 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
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c3
-rw-r--r--kernel/rcu/tree_plugin.h5
2 files changed, 5 insertions, 3 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 63032e5620b9..82838e93b498 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 7e291ce0a1d6..d5b38c28abd1 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;