linux-kernel - Re: [patch] Re: [regression bisect -next] BUG: using smp_processor_id() in preemptible [00000000] code: rmmod

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Date:	Thu, 29 Oct 2009 08:41:45 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	hpa@...or.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de
Subject: Re: [patch] Re: [regression bisect -next] BUG: using
 smp_processor_id() in preemptible [00000000] code: rmmod

On Thu, 2009-10-29 at 11:48 +0100, Mike Galbraith wrote:
> On Thu, 2009-10-29 at 10:19 +0100, Mike Galbraith wrote:
> > On Thu, 2009-10-29 at 10:14 +0100, Ingo Molnar wrote:
> > 
> > > hm, the problem is kthread_bind(). It is rummaging around in scheduler 
> > > internals without holding the runqueue lock - and this now got exposed. 
> > > Even though it is operating on (supposedly ...) inactive tasks, the guts 
> > > of that function should be moved into sched.c and it should be fixed to 
> > > have proper locking.
> > 
> > Yeah, I was thinking that nobody should ever be able to hit that without
> > it being a bug.. but wimped out.
> 
> How about so?
> 
> sched: Move the body of kthread_bind() to sched.c.
> 
> Eric Paris reported that commit f685ceacab07d3f6c236f04803e2f2f0dbcc5afb
> causes boot time PREEMPT_DEBUG complaints.
> 
> [    4.590699] BUG: using smp_processor_id() in preemptible [00000000] code: rmmod/1314
> [    4.593043] caller is task_hot+0x86/0xd0
> [    4.593872] Pid: 1314, comm: rmmod Tainted: G        W  2.6.32-rc3-fanotify #127
> [    4.595443] Call Trace:
> [    4.596177]  [<ffffffff812ad35b>] debug_smp_processor_id+0x11b/0x120
> [    4.597337]  [<ffffffff81051d66>] task_hot+0x86/0xd0
> [    4.598320]  [<ffffffff81066275>] set_task_cpu+0x115/0x270
> [    4.599368]  [<ffffffff810985ab>] kthread_bind+0x6b/0x100
> [    4.600354]  [<ffffffff810914f0>] start_workqueue_thread+0x30/0x60
> [    4.601545]  [<ffffffff810941dd>] __create_workqueue_key+0x18d/0x2f0
> [    4.602526]  [<ffffffff810d9bee>] stop_machine_create+0x4e/0xd0
> [    4.603811]  [<ffffffff810c5818>] sys_delete_module+0x98/0x250
> [    4.604922]  [<ffffffff810e2505>] ? audit_syscall_entry+0x205/0x290
> [    4.606202]  [<ffffffff81013202>] system_call_fastpath+0x16/0x1b
> 
> Since kthread_bind() messes with scheduler internals, move the body to sched.c,
> and lock the runqueue.
> 
> Signed-off-by: Mike Galbraith <efault@....de>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Reported-by: Eric Paris <eparis@...hat.com>

Nothing complains.

Tested-by: Eric Paris <eparis@...hat.com>

Now if I just knew why -next kernels under kvm seem to randomly corrupt
memory and eventually start taking NMI's, then I'd be happy.

-Eric

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