On Sun, Jan 10, 2021 at 09:13:18PM -0800, Paul E. McKenney wrote: > On Mon, Jan 11, 2021 at 01:40:14AM +0100, Frederic Weisbecker wrote: > > On Sat, Jan 09, 2021 at 03:05:33AM +0100, Frederic Weisbecker wrote: > > > 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@xxxxxxxxxx> > > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > > Cc: Ingo Molnar<mingo@xxxxxxxxxx> > > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > --- > > > kernel/entry/common.c | 6 ++++++ > > > kernel/rcu/tree.c | 12 +++++++----- > > > 2 files changed, 13 insertions(+), 5 deletions(-) > > > > > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > > > index 378341642f94..8f3292b5f9b7 100644 > > > --- a/kernel/entry/common.c > > > +++ b/kernel/entry/common.c > > > @@ -178,6 +178,9 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, > > > /* Architecture specific TIF work */ > > > arch_exit_to_user_mode_work(regs, ti_work); > > > > > > + /* Check if any of the above work has queued a deferred wakeup */ > > > + rcu_nocb_flush_deferred_wakeup(); > > > > So this needs to be moved to the IRQs disabled section, just a few lines later, > > otherwise preemption may schedule another task that in turn do call_rcu() and create > > new deferred wake up (thank Paul for the warning). Not to mention moving to > > another CPU with its own deferred wakeups to flush... > > > > I'll fix that for the next version. > > Ah, so it was not just my laptop dying, then! ;-) Note that it fixes the "smp_processor_id() in preemptible" warnings you reported but it shouldn't fix the other issues.
