On Tue, Dec 22, 2020 at 05:19:51PM +0100, Rafael J. Wysocki wrote: > On 12/22/2020 2:37 AM, Frederic Weisbecker wrote: > > With Paul, we've been thinking that the idle loop wasn't twisted enough > > yet to deserve 2020. > > > > rcutorture, after some recent parameter changes, has been complaining > > about a hung task. > > > > It appears that rcu_idle_enter() may wake up a NOCB kthread but this > > happens after the last generic need_resched() check. Some cpuidle drivers > > fix it by chance but many others don't. > > > > Here is a proposed bunch of fixes. I will need to also fix the > > rcu_user_enter() case, likely using irq_work, since nohz_full requires > > irq work to support self IPI. > > > > Also more generally, this raise the question of local task wake_up() > > under disabled interrupts. When a wake up occurs in a preempt disabled > > section, it gets handled by the outer preempt_enable() call. There is no > > similar mechanism when a wake up occurs with interrupts disabled. I guess > > it is assumed to be handled, at worst, in the next tick. But a local irq > > work would provide instant preemption once IRQs are re-enabled. Of course > > this would only make sense in CONFIG_PREEMPTION, and when the tick is > > disabled... > > > > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git > > sched/idle > > > > HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235 > > > > Thanks, > > Frederic > > --- > > > > Frederic Weisbecker (4): > > sched/idle: Fix missing need_resched() check after rcu_idle_enter() > > cpuidle: Fix missing need_resched() check after rcu_idle_enter() > > ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter() > > ACPI: processor: Fix missing need_resched() check after rcu_idle_enter() > > > > > > arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++- > > drivers/acpi/processor_idle.c | 10 ++++++++-- > > drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++-------- > > kernel/sched/idle.c | 18 ++++++++++++------ > > 4 files changed, 51 insertions(+), 17 deletions(-) > > Please feel free to add > > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > to all patches in the series. I would guess that they will take some other path to mainline, but I have queued these to cut down on rcutorture's whining. ;-) Thanx, Paul
