netdev - Re: [Bugme-new] [Bug 8132] New: pptp server lockup in ppp_asynctty

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Date:	Fri, 9 Mar 2007 11:21:43 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	"Yuriy N\. Shkandybin" <jura@...ams.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	"bugme-daemon\@kernel-bugs\.osdl\.org" 
	<bugme-daemon@...zilla.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [Bugme-new] [Bug 8132] New: pptp server lockup in   ppp_asynctty_receive()

On Fri, Mar 09, 2007 at 11:40:04AM +0300, Yuriy N. Shkandybin wrote:
...
> I already have
> CONFIG_PROVE_LOCKING=y
> # CONFIG_4KSTACKS is not set
> .config is at
> http://bugzilla.kernel.org/attachment.cgi?id=10660&action=view
> Also all information i've provied was recieved by serial console and it's 
> not hand writing.

Maybe you cut too much (lines before a bug could be meaningful
- if there are some secret data - try to mask only them).
And there is no real lockdep diagnose, so I wasn't sure.
Dump registers at the end looks incomplete (no ESP info), too.
So, this all made me think - it's cut because it's from the screen.
Very sorry!!!

> I've checked logs and right before lockup there is oops in syslog
> Mar  5 21:50:44 vpn2 skb_under_panic: text:c02248a2 len:207 put:1 

As a matter of fact the first bug is the most interesting
and everything after could be only some aftereffect.
This skb_under_panic message could change all diagnose:
it's not necessarily a locking problem.
On the other hand this could be even harder to diagnose
than locking...

> head:db96e22c data:db96e22b tail:db96e2fa end:db96e82c dev:<NULL>
> Mar  5 21:50:44 vpn2 ------------[ cut here ]------------

Why?! We don't even know if there was some config pending here.

> Mar  5 21:50:44 vpn2 kernel BUG at net/core/skbuff.c:112!
...
> Another thing - when i`ve changed HZ from 100 too 300 there is no such 
> lockups for few days.

You wrote it had been since several kernel releases, so it
shouldn't be the case, but anyway - it would be interesting
to check HZ 100 but with clean and more current kernel version
e.g. 2.6.21-rc3.

Thanks & regards,
Jarek P.
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