linux-kernel - Re: 2.6.21-mm2 - 100% CPU on ksoftirqd/1

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Date:	Wed, 09 May 2007 12:08:43 -0400
From:	Valdis.Kletnieks@...edu
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.21-mm2 - 100% CPU on ksoftirqd/1

On Wed, 09 May 2007 01:23:22 PDT, Andrew Morton said:
> ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21/2.6.21-mm2/

Boots up to multiuser mostly OK.  However...

It comes up with a screaming ksoftirqd - usually /1 but one boot had /0.
Just sitting there, 100% CPU according to 'top'.  Tried 'echo t > /proc/sysrq-trigger' to get
a trace, but it was always running on the other CPU - even after I reniced
it down to 19 and launched 2 'for(;;)' C programs to suck the cycles.  It would
be failing to get any CPU - until I did the 'echo t' and then it would be
"running" again.  Anybody got any good debugging ideas here?

Oddly enough, the kernel panic I was seeing at X server shutdown, related to
-x86_64-mm-reloc64-__pa-and-__pa_symbol-address-space-separation.patch,
seems to be gone now (not extensively tested - but it did survive one shutdown
without crashing at a point that *had* been a 100% fatal from -rc5-mm3 to 21-mm1.
I wish I understood why.

Replicated with a boot to single-user and an untainted kernel - by that point,
it was spinning at 100% already.

Any ideas how to debug this one?  

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