linux-kernel - Re: 2.6.25-rc: complete lockup on boot/start of X (bisected)

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Message-Id: <1206299168.6437.119.camel@lappy>
Date:	Sun, 23 Mar 2008 20:06:08 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 2.6.25-rc: complete lockup on boot/start of X (bisected)

On Sun, 2008-03-23 at 19:46 +0100, Marcin Slusarz wrote:

> 4 different lockups:
> http://alan.umcs.lublin.pl/~mslusarz/kernel/2008.03.23-lockup/ 

Brilliant, these are extremely helpful.

What seems to happen is a classic xtime deadlock, doing a xtime
seq_readlock while holding a seq_writelock.

Only need to figure out _why_ that is happening....

> Are there any downsides of using nmi_watchdog=2 all the time?

Some machines are said to not boot due to NMIs, hence the default is
off, but afaik, _if_ it works there are no downsides aside from the
slight NMI handling overhead.

> ps: Documentation/nmi_watchdog.txt says: "Currently, local APIC mode
> (nmi_watchdog=2) does not work on x86-64.". It's not true, so maybe someone
> should update this file?

Care to send a patch to the x86 maintainers? :-)

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