Messages in this thread | | | Date | Wed, 27 Jul 2016 10:06:13 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 1/1] stop_machine: touch_nmi_watchdog() after MULTI_STOP_PREPARE |
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On Tue, 26 Jul 2016, Oleg Nesterov wrote: > Suppose that stop_machine(fn) hangs because fn() hangs. In this case NMI > hard-lockup can be triggered on another CPU which does nothing wrong and > the trace from nmi_panic() won't help to investigate the problem. > > And this change "fixes" the problem we (seem to) hit in practice. > > - stop_two_cpus(0, 1) races with show_state_filter() running on CPU_0. > > - CPU_1 already spins in MULTI_STOP_PREPARE state, it detects the soft > lockup and tries to report the problem. > > - show_state_filter() enables preemption, CPU_0 calls multi_cpu_stop() > which goes to MULTI_STOP_DISABLE_IRQ state and disables interrupts. > > - CPU_1 spends more than 10 seconds trying to flush the log buffer to > the slow serial console. > > - NMI interrupt on CPU_0 (which now waits for CPU_1) calls nmi_panic(). > > Reported-by: Wang Shu <shuwang@redhat.com> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> --- > kernel/stop_machine.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c > index a467e6c..4a1ca5f 100644 > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -21,6 +21,7 @@ > #include <linux/smpboot.h> > #include <linux/atomic.h> > #include <linux/lglock.h> > +#include <linux/nmi.h> > > /* > * Structure to determine completion condition and record errors. May > @@ -209,6 +210,13 @@ static int multi_cpu_stop(void *data) > break; > } > ack_state(msdata); > + } else if (curstate > MULTI_STOP_PREPARE) { > + /* > + * At this stage all other CPUs we depend on must spin > + * in the same loop. Any reason for hard-lockup should > + * be detected and reported on their side. > + */ > + touch_nmi_watchdog(); > } > } while (curstate != MULTI_STOP_EXIT); > > -- > 2.5.0 > > >
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