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mx.google.com; dkim=pass header.i=@microsoft.com header.s=selector1 header.b=C5nVL2H6; spf=pass (google.com: domain of decui@microsoft.com designates 104.47.126.104 as permitted sender) smtp.mailfrom=decui@microsoft.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=microsoft.com Authentication-Results: mx.google.com; dkim=pass header.i=@microsoft.com header.s=selector1 header.b=C5nVL2H6; spf=pass (google.com: domain of decui@microsoft.com designates 104.47.126.104 as permitted sender) smtp.mailfrom=decui@microsoft.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=microsoft.com From: Dexuan Cui To: Frederic Weisbecker , Ingo Molnar , Andrew Morton , Thomas Gleixner , Linus Torvalds , Dmitry Vyukov CC: Linux Kernel Mailing List , Peter Zijlstra , Greg Kroah-Hartman , KY Srinivasan , Jork Loeser , Rakib Mullick , Alexey Dobriyan , Josh Poulson , "Michael Kelley (EOSG)" Subject: [PATCH] tick/broadcast: Use for_each_cpu() specially on UP kernels Thread-Topic: [PATCH] tick/broadcast: Use for_each_cpu() specially on UP kernels Thread-Index: AdPshQLk7bbHW17pTd+qmP1UgjaPIA== Date: Tue, 15 May 2018 19:52:50 +0000 Message-ID: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=True; 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This causes an unexpected PIT interrupt storm on a UP kernel running in an SMP virtual machine on Hyper-V, and as a result, the virtual machine can suffer from a strange random delay of 1~2= 0 minutes during boot-up, and sometimes it can hang forever. Link: https://lkml.org/lkml/2018/5/9/63 Link: https://lkml.org/lkml/2018/5/15/747 Signed-off-by: Dexuan Cui Cc: stable@vger.kernel.org --- Some part of the changelog and comments are copied from=20 Thomas Gleixner's 115ef3b7e61a ("watchdog/hardlockup/perf: Cure UP damage")= :-) kernel/time/tick-broadcast.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index b398c2e..2fc59ad 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -612,6 +612,14 @@ static void tick_handle_oneshot_broadcast(struct clock= _event_device *dev) now =3D ktime_get(); /* Find all expired events */ for_each_cpu(cpu, tick_broadcast_oneshot_mask) { +#ifndef CONFIG_SMP + /* + * Required because for_each_cpu() reports unconditionally + * CPU0 as set on UP kernels. + */ + if (cpumask_empty(tick_broadcast_oneshot_mask)) + break; +#endif td =3D &per_cpu(tick_cpu_device, cpu); if (td->evtdev->next_event <=3D now) { cpumask_set_cpu(cpu, tmpmask); --=20 2.7.4