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Date: Tue, 11 Jan 2011 14:45:04 -0500
Message-ID: <AANLkTikPoEjHRXjqVkSopCjUcyp7AauvFAfaVN_8T0qG@mail.gmail.com>
Subject: Re: Locking problem reported for mainline
From: Bob Copeland <me@bobcopeland.com>
To: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Christian Lamparter <chunkeey@googlemail.com>,
	wireless <linux-wireless@vger.kernel.org>
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On Tue, Jan 11, 2011 at 11:31 AM, Larry Finger
<Larry.Finger@lwfinger.net> wrote:
> Is there a document that explains what the meaning of these semantics?
>
> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> kdostartupconfi/3502 [HC1[1]:SC0[0]:HE0:SE1] takes:
> ?(&(&list->lock)->rlock#5){?.-...}, at: [<ffffffff812995c6>]
> skb_queue_tail+0x26/0x60
> {HARDIRQ-ON-W} state was registered at:

I'm not sure about all the HC1[1]:SC0[0] etc stuff, but check out
Documentation/lockdep-design.txt for the basics.

In this case, someone took a lock with interrupts enabled (HARDIRQ-ON-W)
while someone else took it in a hard IRQ context (IN-HARDIRQ-W) where
they are normally disabled.  The problem of course is:

cpu0:
spin_lock(&foo);
do some stuff protected by foo;

----> interrupt happens here
   spin_lock(&foo);  /* darn, deadlock! */
   other stuff;
   spin_unlock(&foo);
<----

spin_unlock(&foo);

Could be a missing _irqsave() if it's not, as Stanislaw suggested, a false
positive.

-- 
Bob Copeland %% www.bobcopeland.com