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Mon, 21 May 2018 17:14:50 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dexuan Cui , Thomas Gleixner , Josh Poulson , "Michael Kelley (EOSG)" , Peter Zijlstra , Frederic Weisbecker , Rakib Mullick , Jork Loeser , Andrew Morton , KY Srinivasan , Linus Torvalds , Alexey Dobriyan , Dmitry Vyukov Subject: [PATCH 4.9 28/87] tick/broadcast: Use for_each_cpu() specially on UP kernels Date: Mon, 21 May 2018 23:11:04 +0200 Message-Id: <20180521210422.947603409@linuxfoundation.org> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180521210420.222671977@linuxfoundation.org> References: <20180521210420.222671977@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dexuan Cui 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 Signed-off-by: Thomas Gleixner Cc: Josh Poulson Cc: "Michael Kelley (EOSG)" Cc: Peter Zijlstra Cc: Frederic Weisbecker Cc: stable@vger.kernel.org Cc: Rakib Mullick Cc: Jork Loeser Cc: Greg Kroah-Hartman Cc: Andrew Morton Cc: KY Srinivasan Cc: Linus Torvalds Cc: Alexey Dobriyan Cc: Dmitry Vyukov 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: Greg Kroah-Hartman --- 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);