Re: rcu warning caused by [sched: Fix race between task_group and sched_task_group]

From: Paul E. McKenney
Date: Wed Nov 19 2014 - 14:08:34 EST


On Wed, Nov 19, 2014 at 11:09:46AM +0100, Heiko Carstens wrote:
> Hi Kirill,
>
> the problem below has already been reported here:
> https://lkml.org/lkml/2014/11/11/505
>
> but seems there is still no fix available upstream?
> Would be good to have it soon, since this basically renders lockdep unusable.

This one fixes this bug for me:

https://lkml.org/lkml/2014/11/4/613

Thanx, Paul

> [ 0.173906] ===============================
> [ 0.173907] [ INFO: suspicious RCU usage. ]
> [ 0.173909] 3.18.0-rc5 #15 Not tainted
> [ 0.173909] -------------------------------
> [ 0.173910] kernel/sched/core.c:7449 suspicious rcu_dereference_check() usage!
> [ 0.173912]
> other info that might help us debug this:
> [ 0.173913]
> rcu_scheduler_active = 1, debug_locks = 0
> [ 0.173914] 2 locks held by swapper/0/0:
> [ 0.173915] #0: (&p->pi_lock){......}, at: [<000000000017baae>] task_rq_lock+0x4e/0xf8
> [ 0.173925] #1: (&rq->lock){......}, at: [<000000000017bad6>] task_rq_lock+0x76/0xf8
> [ 0.173928]
> [ 0.173930] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc5 #15
> [ 0.173931] 0000000000b9fb70 0000000000b9fb80 0000000000000002 0000000000000000
> 0000000000b9fc10 0000000000b9fb88 0000000000b9fb88 0000000000112638
> 0000000000000000 00000000009d5b8c 00000000009be240 000000000000000b
> 0000000000b9fbd0 0000000000b9fb70 0000000000000000 0000000000000000
> 0000000000000000 0000000000112638 0000000000b9fb70 0000000000b9fbd0
> [ 0.173944] Call Trace:
> [ 0.173947] ([<000000000011251c>] show_trace+0xf4/0x158)
> [ 0.173949] [<00000000001125ea>] show_stack+0x6a/0xe8
> [ 0.173952] [<0000000000807ac2>] dump_stack+0x82/0xb0
> [ 0.173955] [<000000000018700a>] sched_move_task+0x20a/0x210
> [ 0.173959] [<0000000000203bf0>] cgroup_post_fork+0x60/0x148
> [ 0.173963] [<000000000014c5b8>] copy_process.part.46+0xfe8/0x1bc8
> [ 0.173964] [<000000000014d39c>] do_fork+0x104/0x7d8
> [ 0.173965] [<000000000014dab6>] kernel_thread+0x46/0x58
> [ 0.173968] [<00000000007fe890>] rest_init+0x38/0x170
> [ 0.173971] [<0000000000c45b40>] start_kernel+0x460/0x470
> [ 0.173972] [<0000000000100020>] _stext+0x20/0x80
> [ 0.173973] INFO: lockdep is turned off.
>
> caused by (bisected):
>
> commit eeb61e53ea19be0c4015b00b2e8b3b2185436f2b
> Author: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> Date: Mon Oct 27 14:18:25 2014 +0400
>
> sched: Fix race between task_group and sched_task_group
>
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