linux-kernel - Re: Linux 3.16-rc6

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Message-ID: <CA+55aFzPs4uF=eR7jCnpyBtgWNRkX-uDfXeo5u34VEvT8_yyzw@mail.gmail.com>
Date:	Wed, 23 Jul 2014 17:37:43 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: Linux 3.16-rc6

On Wed, Jul 23, 2014 at 2:53 AM, Borislav Petkov <bp@...en8.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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