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SubjectRe: Linux 3.16-rc6
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On Wed, Jul 23, 2014 at 2:53 AM, Borislav Petkov <bp@alien8.de> wrote:
>
> Well, it looks like we f*cked up something after -rc5 since I'm starting
> to see lockdep splats all over the place which I didn't see before. I'm
> running rc6 + tip/master.
>
> There was one in r8169 yesterday:
>
> https://lkml.kernel.org/r/20140722081840.GA6462@pd.tnic
>
> and now I'm seeing the following in a kvm guest. I'm adding some more
> lists to CC which look like might be related, judging from the stack
> traces.

Hmm. I'm not seeing the reason for this.

> [ 31.704282] [ INFO: possible irq lock inversion dependency detected ]
> [ 31.704282] 3.16.0-rc6+ #1 Not tainted
> [ 31.704282] ---------------------------------------------------------
> [ 31.704282] Xorg/3484 just changed the state of lock:
> [ 31.704282] (tasklist_lock){.?.+..}, at: [<ffffffff81184b19>] send_sigio+0x59/0x1b0
> [ 31.704282] but this lock took another, HARDIRQ-unsafe lock in the past:
> [ 31.704282] (&(&p->alloc_lock)->rlock){+.+...}

Ok, so the claim is that there's a 'p->alloc_lock' (ie "task_lock()")
that is inside the tasklist_lock, which would indeed be wrong. But I'm
not seeing it. The "shortest dependencies" thing seems to imply
__set_task_comm(), but that only takes task_lock.

Unless there is something in tip/master. Can you check that this is
actually in plain -rc6?

Or maybe I'm just blind. Those lockdep splats are easy to get wrong.
Adding PeterZ and Ingo to the list just because they are my lockdep
go-to people.

Linus


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