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

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Date:	Sat, 24 Jan 2009 08:36:35 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	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>,
	Darren Hart <dvhltc@...ibm.com>
Subject: Re: kernel BUG at fs/ext/super.c:428

On Wed, 2009-01-21 at 12:10 -0800, Pallipadi, Venkatesh wrote:
> On Wed, 2009-01-14 at 13:20 -0800, Theodore Tso wrote:
> > On Wed, Jan 14, 2009 at 08:29:37PM +0100, Peter Zijlstra wrote:
> > > > 38d47c1b7075bd7ec3881141bb3629da58f88dab is first bad commit
> > > > commit 38d47c1b7075bd7ec3881141bb3629da58f88dab
> > > > Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > > Date:   Fri Sep 26 19:32:20 2008 +0200
> > > >
> > > >     futex: rely on get_user_pages() for shared futexes
> > > >
> > > >     On the way of getting rid of the mmap_sem requirement for shared futexes,
> > > >     start by relying on get_user_pages().
> > > >
> > > >     Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > >     Acked-by: Nick Piggin <nickpiggin@...oo.com.au>
> > > >     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > > >
> > > However does a futex change make ext3 crap its pants?
> > 
> > I agree, this doesn't make much sense.  I've looked at the patch, and
> > I don't see how this would cause an ext3 orphaned-inode list handling
> > problem
> > 
> > Are you sure the bisect was done correctly?  Have you tried reverting
> > that one commit, or otherwise conclusively shown that a kernel with
> > this commit fails, and one without this commit works just fine?
> > 
> 
> Unfortunately, I cannot revert this patch alone from upstream git.
> But I consistently see
> upstream git: Always produces this oops on reboot
> checkout of 38d47c1b: Always produces this oops on reboot
> checkout of 94aca1da (one patch before the above commit): Reboots fine
> without the oops.
> 
> This is petty specific to the particular userspace, looks like.
> I only see this on SLES10 installation. Also, I need a non-root user
> logged in at least once after boot through X to see this problem. I was
> always seeing this as I had autologin on local terminal and was remotely
> rebooting the system. If I just boot to init 3 or boot to init 5 with no
> user logged in or boot to init 5 with root logged in, I do not see this
> problem.

Ted, could this happen due an extra iput()?

In that case, Venki, does the below patch fix it?

Credit goes to Darren for spotting this.

---
 kernel/futex.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

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);
 
 out_put_keys:
 	put_futex_key(fshared, &key2);


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