From: Frederic Weisbecker frederic@kernel.org
commit a554ba288845fd3f6f12311fd76a51694233458a upstream.
Time limit only makes sense when callbacks are serviced in softirq mode because:
_ In case we need to get back to the scheduler, cond_resched_tasks_rcu_qs() is called after each callback.
_ In case some other softirq vector needs the CPU, the call to local_bh_enable() before cond_resched_tasks_rcu_qs() takes care about them via a call to do_softirq().
Therefore, make sure the time limit only applies to softirq mode.
Reviewed-by: Valentin Schneider valentin.schneider@arm.com Tested-by: Valentin Schneider valentin.schneider@arm.com Tested-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Frederic Weisbecker frederic@kernel.org Cc: Valentin Schneider valentin.schneider@arm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Sebastian Andrzej Siewior bigeasy@linutronix.de Cc: Josh Triplett josh@joshtriplett.org Cc: Joel Fernandes joel@joelfernandes.org Cc: Boqun Feng boqun.feng@gmail.com Cc: Neeraj Upadhyay neeraju@codeaurora.org Cc: Uladzislau Rezki urezki@gmail.com Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Paul E. McKenney paulmck@kernel.org [UR: backport to 5.15-stable] Signed-off-by: Uladzislau Rezki (Sony) urezki@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/rcu/tree.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-)
--- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2476,7 +2476,7 @@ static void rcu_do_batch(struct rcu_data div = READ_ONCE(rcu_divisor); div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div; bl = max(rdp->blimit, pending >> div); - if (unlikely(bl > 100)) { + if (in_serving_softirq() && unlikely(bl > 100)) { long rrn = READ_ONCE(rcu_resched_ns);
rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn; @@ -2517,6 +2517,18 @@ static void rcu_do_batch(struct rcu_data if (count >= bl && (need_resched() || (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) break; + + /* + * Make sure we don't spend too much time here and deprive other + * softirq vectors of CPU cycles. + */ + if (unlikely(tlimit)) { + /* only call local_clock() every 32 callbacks */ + if (likely((count & 31) || local_clock() < tlimit)) + continue; + /* Exceeded the time limit, so leave. */ + break; + } } else { local_bh_enable(); lockdep_assert_irqs_enabled(); @@ -2524,18 +2536,6 @@ static void rcu_do_batch(struct rcu_data lockdep_assert_irqs_enabled(); local_bh_disable(); } - - /* - * Make sure we don't spend too much time here and deprive other - * softirq vectors of CPU cycles. - */ - if (unlikely(tlimit)) { - /* only call local_clock() every 32 callbacks */ - if (likely((count & 31) || local_clock() < tlimit)) - continue; - /* Exceeded the time limit, so leave. */ - break; - } }
local_irq_save(flags);