linux-ext4 - Re: kernel BUG at fs/ext/super.c:428

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Date:	Mon, 26 Jan 2009 17:46:11 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Theodore Tso <tytso@....EDU>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: kernel BUG at fs/ext/super.c:428

On Mon, 2009-01-26 at 08:39 -0800, Darren Hart wrote:

> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index f89d373..f4132ab 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -929,7 +929,7 @@ out_unlock:
> > 
> >  	/* drop_futex_key_refs() must be called outside the spinlocks. */
> >  	while (--drop_count >= 0)
> > -		drop_futex_key_refs(&key1);
> > +		drop_futex_key_refs(&key2);
> 
> Unfortunately, I realized later that this code was indeed correct and I 
> asked Ingo to pull my patch implementing the above change.  Quoting my 
> previous mail on the subject:
> 
> "I believe what is happening here is that the requeue loop requeues each 
> waiter from one futex (key1) to another (key2).  It rightly takes a 
> reference to the futex at key2 and then decrements the references to 
> key1 by drop_count (since the waiters now reference key2, not key1). 
> The newly taken key2 references will be dropped in futex_wait() when 
> each waiter is woken up and takes the futex."

Argh, that wants a comment..

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