[PATCH 4/4] ACPI: processor: Fix missing need_resched() check after rcu_idle_enter()
From: Frederic Weisbecker
Date: Mon Dec 21 2020 - 20:38:38 EST
Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
kthread (rcuog) to be serviced.
Usually a wake up happening while running the idle task is spotted in
one of the need_resched() checks carefully placed within the idle loop
that can break to the scheduler.
Unfortunately within acpi_idle_enter_bm() the call to rcu_idle_enter()
is already beyond the last generic need_resched() check. The cpu idle
implementation happens to be ok because it ends up calling
mwait_idle_with_hints() or acpi_safe_halt() which both perform their own
need_resched() checks. But the suspend to idle implementation doesn't so
it may suspend the CPU with a resched request unhandled, leaving the
task hanging.
Fix this with performing a last minute need_resched() check after
calling rcu_idle_enter().
Reported-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Fixes: 1fecfdbb7acc (ACPI: processor: Take over RCU-idle for C3-BM idle)
Cc: stable@xxxxxxxxxxxxxxx
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar<mingo@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
drivers/acpi/processor_idle.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index d93e400940a3..c4939c49d972 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -604,8 +604,14 @@ static int acpi_idle_enter_bm(struct cpuidle_driver *drv,
}
rcu_idle_enter();
-
- acpi_idle_do_entry(cx);
+ /*
+ * Last need_resched() check must come after rcu_idle_enter()
+ * which may wake up RCU internal tasks. mwait_idle_with_hints()
+ * and acpi_safe_halt() have their own checks but s2idle
+ * implementation doesn't.
+ */
+ if (!need_resched())
+ acpi_idle_do_entry(cx);
rcu_idle_exit();
--
2.25.1