linux-kernel - Re: RCU detected CPU 0 stall after panic on sparc64

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Message-ID: <20091214202556.GC6679@linux.vnet.ibm.com>
Date:	Mon, 14 Dec 2009 12:25:56 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	mroos@...ux.ee, linux-kernel@...r.kernel.org,
	sparclinux@...r.kernel.org
Subject: Re: RCU detected CPU 0 stall after panic on sparc64

On Sat, Dec 12, 2009 at 01:40:02AM -0800, David Miller wrote:
> From: Meelis Roos <mroos@...ux.ee>
> Date: Sat, 12 Dec 2009 10:54:19 +0200 (EET)
> 
> > I tried 2.6.32 git gaad3bf0 on a SMP sparc64 machine (Ultra Enterprise 
> > 250). For some reason my disks were not found (not important in this 
> > bugreport) and this resulted in panic (cannnot mount root). However, the 
> > machine kept going and got the below messages (RCU detected CPU 0 stall 
> > (t=1000 jiffies)) from timer interrupts.
> > 
> > This seems to be like a bug in RCU vs panic.
> 
> It's normal actually.  A panic() just loops forever and the cpu never
> goes through an RCU grace period again as a result, and this triggers
> the debugging timer that detects this condition.
> 
> Probably the panic() code should disable that assertion check.

Hmmm...  At first glance, it looks like RCU should put a notifier onto
the panic_notifier_list to disable this check.  Or is there some global
variable that I can check?

							Thanx, Paul
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