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From: tip-bot for Dexuan Cui <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: tglx@linutronix.de, fweisbec@gmail.com, kys@microsoft.com,
	dvyukov@google.com, adobriyan@gmail.com,
	gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
	mingo@kernel.org, akpm@linux-foundation.org,
	torvalds@linux-foundation.org, rakib.mullick@gmail.com,
	decui@microsoft.com, Michael.H.Kelley@microsoft.com,
	hpa@zytor.com, jopoulso@microsoft.com, peterz@infradead.org,
	Jork.Loeser@microsoft.com
Subject: [tip:timers/urgent] tick/broadcast: Use for_each_cpu() specially on UP kernels
Date: Tue, 15 May 2018 13:48:55 -0700	[thread overview]
Message-ID: <tip-5596fe34495cf0f645f417eb928ef224df3e3cb4@git.kernel.org> (raw)
In-Reply-To: <KL1P15301MB0006FA63BC22BEB64902EAA0BF930@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM>

Commit-ID:  5596fe34495cf0f645f417eb928ef224df3e3cb4
Gitweb:     https://git.kernel.org/tip/5596fe34495cf0f645f417eb928ef224df3e3cb4
Author:     Dexuan Cui <decui@microsoft.com>
AuthorDate: Tue, 15 May 2018 19:52:50 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 15 May 2018 22:45:54 +0200

tick/broadcast: Use for_each_cpu() specially on UP kernels

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@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM
Link: https://lkml.kernel.org/r/KL1P15301MB0006FA63BC22BEB64902EAA0BF930@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM
---
 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 b398c2ea69b2..aa2094d5dd27 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 = 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 <= now) {
 			cpumask_set_cpu(cpu, tmpmask);

      reply	other threads:[~2018-05-15 20:48 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-09  6:24 for_each_cpu() is buggy for UP kernel? Dexuan Cui
2018-05-09 23:20 ` Andrew Morton
2018-05-13 13:35   ` Thomas Gleixner
2018-05-13 18:21 ` Linus Torvalds
2018-05-14  7:28   ` Dmitry Vyukov
2018-05-15  3:02   ` Dexuan Cui
2018-05-15 17:21     ` Linus Torvalds
2018-05-15 20:10       ` Dexuan Cui
2018-05-15 19:52 ` [PATCH] tick/broadcast: Use for_each_cpu() specially on UP kernels Dexuan Cui
2018-05-15 20:48   ` tip-bot for Dexuan Cui [this message]

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