linux-kernel - Re: recent -git: BUG in free_thread

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Message-ID: <b647ffbd0807231422w546e59e9p8362ee798b169a25@mail.gmail.com>
Date:	Wed, 23 Jul 2008 23:22:24 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Suresh Siddha" <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Subject: Re: recent -git: BUG in free_thread_xstate

2008/7/23 Vegard Nossum <vegard.nossum@...il.com>:
> On Wed, Jul 23, 2008 at 10:31 PM, Suresh Siddha
> <suresh.b.siddha@...el.com> wrote:
>> On Wed, Jul 23, 2008 at 01:07:04PM -0700, Vegard Nossum wrote:
>>> Hi,
>>>
>>> I just got this on c010b2f76c3032e48097a6eef291d8593d5d79a6 (-git from
>>> yesterday):
>>
>> Do you see this in 2.6.26 aswell? I suspect it is coming from post 2.6.26
>> changes.
>>
>
> Humm... I got something different now on plain 2.6.26:
>
> ------------[ cut here ]------------
> WARNING: at kernel/sched_fair.c:815 hrtick_start_fair+0x158/0x170()

that's interesting. As a first step and if it's easily reproducible,
would you try something like below?

(hope, it compiles :-)

If it doesn't crash immediately, then 'p' is likely to be a real task
(well, we'll see then with p->comm) and if its cpu is different from
rq->cpu (must be in this case), then we might have a funny race
somewhere...

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -813,6 +813,9 @@ static void hrtick_start_fair(struct rq *rq,
struct task_struct *p)
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        WARN_ON(task_rq(p) != rq);
+       if (task_rq(p) != rq)
+               printk(KERN_ERR "task (%s)'s cpu (%d), rq's (%d)\n",
+                               p->comm, task_cpu(p), rq->cpu);

        if (hrtick_enabled(rq) && cfs_rq->nr_running > 1) {
                u64 slice = sched_slice(cfs_rq, se);

>
> [ ... ]
>

-- 
Best regards,
Dmitry Adamushko
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