| From: Dexuan Cui <decui@microsoft.com> |
| Date: Tue, 15 May 2018 19:52:50 +0000 |
| Subject: tick/broadcast: Use for_each_cpu() specially on UP kernels |
| |
| commit 5596fe34495cf0f645f417eb928ef224df3e3cb4 upstream. |
| |
| for_each_cpu() unintuitively reports CPU0 as set independent of the actual |
| cpumask content on UP kernels. 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 1~20 |
| minutes during boot-up, and sometimes it can hang forever. |
| |
| Protect if by checking whether the cpumask is empty before entering the |
| for_each_cpu() loop. |
| |
| [ tglx: Use !IS_ENABLED(CONFIG_SMP) instead of #ifdeffery ] |
| |
| Signed-off-by: Dexuan Cui <decui@microsoft.com> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Cc: Josh Poulson <jopoulso@microsoft.com> |
| Cc: "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Frederic Weisbecker <fweisbec@gmail.com> |
| Cc: Rakib Mullick <rakib.mullick@gmail.com> |
| Cc: Jork Loeser <Jork.Loeser@microsoft.com> |
| Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Cc: Andrew Morton <akpm@linux-foundation.org> |
| Cc: KY Srinivasan <kys@microsoft.com> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Alexey Dobriyan <adobriyan@gmail.com> |
| Cc: Dmitry Vyukov <dvyukov@google.com> |
| Link: https://lkml.kernel.org/r/KL1P15301MB000678289FE55BA365B3279ABF990@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM |
| Link: https://lkml.kernel.org/r/KL1P15301MB0006FA63BC22BEB64902EAA0BF930@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| kernel/time/tick-broadcast.c | 8 ++++++++ |
| 1 file changed, 8 insertions(+) |
| |
| --- a/kernel/time/tick-broadcast.c |
| +++ b/kernel/time/tick-broadcast.c |
| @@ -585,6 +585,14 @@ again: |
| now = ktime_get(); |
| /* Find all expired events */ |
| for_each_cpu(cpu, tick_broadcast_oneshot_mask) { |
| + /* |
| + * Required for !SMP because for_each_cpu() reports |
| + * unconditionally CPU0 as set on UP kernels. |
| + */ |
| + if (!IS_ENABLED(CONFIG_SMP) && |
| + cpumask_empty(tick_broadcast_oneshot_mask)) |
| + break; |
| + |
| td = &per_cpu(tick_cpu_device, cpu); |
| if (td->evtdev->next_event.tv64 <= now.tv64) { |
| cpumask_set_cpu(cpu, tmpmask); |
