Re: sched: spinlock recursion in sched_rr_get_interval

[Li Bin <huawei.libin@huawei.com>]

On 2014/7/8 4:05, Peter Zijlstra wrote:
> On Mon, Jul 07, 2014 at 09:55:43AM -0400, Sasha Levin wrote:
>> I've also had this one, which looks similar:
>>
>> [10375.005884] BUG: spinlock recursion on CPU#0, modprobe/10965
>> [10375.006573]  lock: 0xffff8803a0fd7740, .magic: dead4ead, .owner: modprobe/10965, .owner_cpu: 15
>> [10375.007412] CPU: 0 PID: 10965 Comm: modprobe Tainted: G        W      3.16.0-rc3-next-20140704-sasha-00023-g26c0906-dirty #765
> 
> Something's fucked; so we have:
> 
> debug_spin_lock_before()
> 	SPIN_BUG_ON(lock->owner == current, "recursion");
> 

Hello，
Does ACCESS_ONCE() can help this issue? I have no evidence that its lack is
responsible for the issue, but I think here need it indeed. Is that right?

SPIN_BUG_ON(ACCESS_ONCE(lock->owner) == current, "recursion");

Thanks,
		Li Bin

> Causing that, _HOWEVER_ look at .owner_cpu and the reporting cpu!! How
> can the lock owner, own the lock on cpu 15 and again contend with it on
> CPU 0. That's impossible.
> 
> About when-ish did you start seeing things like this? Lemme go stare
> hard at recent changes.
>