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 <frede...@kernel.org>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > Cc: Ingo Molnar<mi...@kernel.org>
> > Cc: Paul E. McKenney <paul...@kernel.org>
> > Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> > ---
> > 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! ;-)
Thanx, Paul
