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Date: Mon, 3 Oct 2016 16:42:46 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ingo Molnar <mingo@kernel.org>,
        Byungchul Park <byungchul.park@lge.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Luca Abeni <luca.abeni@unitn.it>, Rik van Riel <riel@redhat.com>,
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        Wanpeng Li <wanpeng.li@hotmail.com>, Yuyang Du <yuyang.du@intel.com>,
        Petr Mladek <pmladek@suse.com>, Jan Kara <jack@suse.cz>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        linux-kernel@vger.kernel.org, Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [PATCH v2 1/7] sched/fair: Update the rq clock before detaching
 tasks
Message-ID: <20161003144246.GD3117@twins.programming.kicks-ass.net>
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On Mon, Oct 03, 2016 at 03:37:45PM +0100, Matt Fleming wrote:
> On Mon, 03 Oct, at 02:49:07PM, Peter Zijlstra wrote:

> > The other is through switched_from() where its far harder (but still
> > possible afaict) to miss the update.
>  
> It was the former callchain.

Yep, just found it ;-)

I seem to hit a few you didn't as well.. let me prod at this a wee bit
more before I add more asserts..


4WARNING: CPU: 0 PID: 1 at ../kernel/sched/sched.h:797 detach_task_cfs_rq+0x6fe/0x930
rq->clock_update_flags < RQCF_ACT_SKIPdModules linked in:
dCPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-00637-g67223e2-dirty #553
dHardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
 ffffc900000cbc00 ffffffff816152c5 ffffc900000cbc50 0000000000000000
 ffffc900000cbc40 ffffffff810d5bab 0000031d00017b00 ffff88042f817b68
 ffff88042dbb0000 ffff88042f817b00 ffff88042dbb0000 ffffffff81c18900
Call Trace:
 [<ffffffff816152c5>] dump_stack+0x67/0x92
 [<ffffffff810d5bab>] __warn+0xcb/0xf0
 [<ffffffff810d5c1f>] warn_slowpath_fmt+0x4f/0x60
 [<ffffffff8110efae>] detach_task_cfs_rq+0x6fe/0x930
 [<ffffffff8110f1f1>] switched_from_fair+0x11/0x20
 [<ffffffff810fde77>] __sched_setscheduler+0x2a7/0xb40
 [<ffffffff810fe779>] _sched_setscheduler+0x69/0x70
 [<ffffffff810ff243>] sched_set_stop_task+0x53/0x90
 [<ffffffff81173703>] cpu_stop_create+0x23/0x30
 [<ffffffff810f90c0>] __smpboot_create_thread.part.2+0xb0/0x100
 [<ffffffff810f91ef>] smpboot_register_percpu_thread_cpumask+0xdf/0x140
 [<ffffffff823c24e7>] ? pid_namespaces_init+0x40/0x40
 [<ffffffff823c254b>] cpu_stop_init+0x64/0x9b
 [<ffffffff8100040d>] do_one_initcall+0x3d/0x150
 [<ffffffff8107763d>] ? print_cpu_info+0x7d/0xe0
 [<ffffffff823a0001>] kernel_init_freeable+0xcc/0x207
 [<ffffffff81a7d8d0>] ? rest_init+0x90/0x90
 [<ffffffff81a7d8de>] kernel_init+0xe/0x100
 [<ffffffff81a89bc7>] ret_from_fork+0x27/0x40
4---[ end trace 90bea7c93d2289cb ]---