4.9-stable review patch. If anyone has any objections, please let me know.
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From: Dexuan Cui decui@microsoft.com
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: stable@vger.kernel.org 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@KL1P15301... Link: https://lkml.kernel.org/r/KL1P15301MB0006FA63BC22BEB64902EAA0BF930@KL1P15301... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/time/tick-broadcast.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -610,6 +610,14 @@ static void tick_handle_oneshot_broadcas 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);