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Message-ID: <lsq.1539530741.413820146@decadent.org.uk>
Date: Sun, 14 Oct 2018 16:25:41 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
"Jork Loeser" <Jork.Loeser@...rosoft.com>,
"Peter Zijlstra" <peterz@...radead.org>,
"Alexey Dobriyan" <adobriyan@...il.com>,
"Dmitry Vyukov" <dvyukov@...gle.com>,
"KY Srinivasan" <kys@...rosoft.com>,
"Josh Poulson" <jopoulso@...rosoft.com>,
"Dexuan Cui" <decui@...rosoft.com>,
"Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
"Linus Torvalds" <torvalds@...ux-foundation.org>,
"Frederic Weisbecker" <fweisbec@...il.com>,
"Rakib Mullick" <rakib.mullick@...il.com>
Subject: [PATCH 3.16 322/366] tick/broadcast: Use for_each_cpu() specially
on UP kernels
3.16.60-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Dexuan Cui <decui@...rosoft.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@...rosoft.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Josh Poulson <jopoulso@...rosoft.com>
Cc: "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Rakib Mullick <rakib.mullick@...il.com>
Cc: Jork Loeser <Jork.Loeser@...rosoft.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: KY Srinivasan <kys@...rosoft.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.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@...adent.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);
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