Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755349Ab3D0J7S (ORCPT ); Sat, 27 Apr 2013 05:59:18 -0400 Received: from e28smtp05.in.ibm.com ([122.248.162.5]:54567 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754807Ab3D0J7R (ORCPT ); Sat, 27 Apr 2013 05:59:17 -0400 Message-ID: <1367056747.6391.15.camel@ThinkPad-T5421.cn.ibm.com> Subject: [RFC PATCH]nohz: Use raw_smp_processor_id() in tick_nohz_task_switch() From: Li Zhong To: LKML Cc: Frederic Weisbecker Date: Sat, 27 Apr 2013 17:59:07 +0800 Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13042709-8256-0000-0000-0000073DAFAB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1979 Lines: 49 I saw following error when testing the latest nohz code on Power: [ 85.295384] BUG: using smp_processor_id() in preemptible [00000000] code: rsyslogd/3493 [ 85.295396] caller is .tick_nohz_task_switch+0x1c/0xb8 [ 85.295402] Call Trace: [ 85.295408] [c0000001fababab0] [c000000000012dc4] .show_stack+0x110/0x25c (unreliable) [ 85.295420] [c0000001fababba0] [c0000000007c4b54] .dump_stack+0x20/0x30 [ 85.295430] [c0000001fababc10] [c00000000044eb74] .debug_smp_processor_id+0xf4/0x124 [ 85.295438] [c0000001fababca0] [c0000000000d7594] .tick_nohz_task_switch+0x1c/0xb8 [ 85.295447] [c0000001fababd20] [c0000000000b9748] .finish_task_switch+0x13c/0x160 [ 85.295455] [c0000001fababdb0] [c0000000000bbe50] .schedule_tail+0x50/0x124 [ 85.295463] [c0000001fababe30] [c000000000009dc8] .ret_from_fork+0x4/0x54 It seems to me that we could just use raw_smp_processor_id() here. Even if the tick_nohz_full_cpu() check is done on a !nohz_full cpu, then the task is moved to another nohz_full cpu, it seems the context switching because of the task moving would call tick_nohz_task_switch() again to evaluate the need for tick. I don't know whether I missed something here. Signed-off-by: Li Zhong --- kernel/time/tick-sched.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index da53c8f..0aa575b 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -251,7 +251,7 @@ void tick_nohz_task_switch(struct task_struct *tsk) { unsigned long flags; - if (!tick_nohz_full_cpu(smp_processor_id())) + if (!tick_nohz_full_cpu(raw_smp_processor_id())) return; local_irq_save(flags); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/