From: Frederic Weisbecker frederic@kernel.org
[ Upstream commit 47b8ff194c1fd73d58dc339b597d466fe48c8958 ]
Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point on resuming to user mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling.
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/20210131230548.32970-5-frederic@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/entry/common.c | 7 +++++++ kernel/rcu/tree.c | 12 +++++++----- 2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c index e289e6773292..d6587e10bd4c 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -174,6 +174,10 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, * enabled above. */ local_irq_disable_exit_to_user(); + + /* Check if any of the above work has queued a deferred wakeup */ + rcu_nocb_flush_deferred_wakeup(); + ti_work = READ_ONCE(current_thread_info()->flags); }
@@ -187,6 +191,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
lockdep_assert_irqs_disabled();
+ /* Flush pending rcuog wakeup before the last need_resched() check */ + rcu_nocb_flush_deferred_wakeup(); + if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f137a599941b..0d8a2e2df221 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -699,13 +699,15 @@ noinstr void rcu_user_enter(void) lockdep_assert_irqs_disabled();
/* - * We may be past the last rescheduling opportunity in the entry code. - * Trigger a self IPI that will fire and reschedule once we resume to - * user/guest mode. + * Other than generic entry implementation, we may be past the last + * rescheduling opportunity in the entry code. Trigger a self IPI + * that will fire and reschedule once we resume in user/guest mode. */ instrumentation_begin(); - if (do_nocb_deferred_wakeup(rdp) && need_resched()) - irq_work_queue(this_cpu_ptr(&late_wakeup_work)); + if (!IS_ENABLED(CONFIG_GENERIC_ENTRY) || (current->flags & PF_VCPU)) { + if (do_nocb_deferred_wakeup(rdp) && need_resched()) + irq_work_queue(this_cpu_ptr(&late_wakeup_work)); + } instrumentation_end();
rcu_eqs_enter(true);