Messages in this thread | | | Date | Mon, 3 Sep 2018 22:04:04 +0930 | From | Kevin Shanahan <> | Subject | Re: REGRESSION: boot stalls on several old dual core Intel CPUs |
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On Mon, Sep 03, 2018 at 11:33:05AM +0200, Peter Zijlstra wrote: > On Mon, Sep 03, 2018 at 10:54:23AM +0200, Peter Zijlstra wrote: > > On Mon, Sep 03, 2018 at 09:38:15AM +0200, Thomas Gleixner wrote: > > > On Mon, 3 Sep 2018, Peter Zijlstra wrote: > > > > On Sat, Sep 01, 2018 at 11:51:26AM +0930, Kevin Shanahan wrote: > > > > > commit 01548f4d3e8e94caf323a4f664eb347fd34a34ab > > > > > Author: Martin Schwidefsky <schwidefsky@de.ibm.com> > > > > > Date: Tue Aug 18 17:09:42 2009 +0200 > > > > > > > > > > clocksource: Avoid clocksource watchdog circular locking dependency > > > > > > > > > > stop_machine from a multithreaded workqueue is not allowed because > > > > > of a circular locking dependency between cpu_down and the workqueue > > > > > execution. Use a kernel thread to do the clocksource downgrade. > > > > > > > > I cannot find stop_machine usage there; either it went away or I need to > > > > like wake up. > > > > > > timekeeping_notify() which is involved in switching clock source uses stomp > > > machine. > > > > ARGH... OK, lemme see if I can come up with something other than > > endlessly spawning that kthread. > > > > A special purpose kthread_worker would make more sense than that. > > Can someone test this?
Boots for me (applied on top of 4.18.5).
Tested-by: Kevin Shanahan <kevin@shanahan.id.au>
> --- > kernel/time/clocksource.c | 28 ++++++++++++++++++++++------ > 1 file changed, 22 insertions(+), 6 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index f74fb00d8064..898976d0082a 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -112,13 +112,28 @@ static int finished_booting; > static u64 suspend_start; > > #ifdef CONFIG_CLOCKSOURCE_WATCHDOG > -static void clocksource_watchdog_work(struct work_struct *work); > +static void clocksource_watchdog_work(struct kthread_work *work); > static void clocksource_select(void); > > static LIST_HEAD(watchdog_list); > static struct clocksource *watchdog; > static struct timer_list watchdog_timer; > -static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); > + > +/* > + * We must use a kthread_worker here, because: > + * > + * clocksource_watchdog_work() > + * clocksource_select() > + * __clocksource_select() > + * timekeeping_notify() > + * stop_machine() > + * > + * cannot be called from a reqular workqueue, because of deadlocks between > + * workqueue and stopmachine. > + */ > +static struct kthread_worker *watchdog_worker; > +static DEFINE_KTHREAD_WORK(watchdog_work, clocksource_watchdog_work); > + > static DEFINE_SPINLOCK(watchdog_lock); > static int watchdog_running; > static atomic_t watchdog_reset_pending; > @@ -158,7 +173,7 @@ static void __clocksource_unstable(struct clocksource *cs) > > /* kick clocksource_watchdog_work() */ > if (finished_booting) > - schedule_work(&watchdog_work); > + kthread_queue_work(watchdog_worker, &watchdog_work); > } > > /** > @@ -199,7 +214,7 @@ static void clocksource_watchdog(struct timer_list *unused) > /* Clocksource already marked unstable? */ > if (cs->flags & CLOCK_SOURCE_UNSTABLE) { > if (finished_booting) > - schedule_work(&watchdog_work); > + kthread_queue_work(watchdog_worker, &watchdog_work); > continue; > } > > @@ -269,7 +284,7 @@ static void clocksource_watchdog(struct timer_list *unused) > */ > if (cs != curr_clocksource) { > cs->flags |= CLOCK_SOURCE_RESELECT; > - schedule_work(&watchdog_work); > + kthread_queue_work(watchdog_worker, &watchdog_work); > } else { > tick_clock_notify(); > } > @@ -418,7 +433,7 @@ static int __clocksource_watchdog_work(void) > return select; > } > > -static void clocksource_watchdog_work(struct work_struct *work) > +static void clocksource_watchdog_work(struct kthread_work *work) > { > mutex_lock(&clocksource_mutex); > if (__clocksource_watchdog_work()) > @@ -806,6 +821,7 @@ static int __init clocksource_done_booting(void) > { > mutex_lock(&clocksource_mutex); > curr_clocksource = clocksource_default_clock(); > + watchdog_worker = kthread_create_worker(0, "cs-watchdog"); > finished_booting = 1; > /* > * Run the watchdog first to eliminate unstable clock sources
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