Re: BUG: unable to handle kernel paging request at virtual address 6b6b6b6f

[Frank van Maarseveen <frankvm@frankvm.com>]

On Tue, Jul 03, 2007 at 03:39:37PM -0400, J. Bruce Fields wrote:
> On Tue, Jul 03, 2007 at 09:17:35AM +0200, Frank van Maarseveen wrote:
> > I've reported this earlier but now I figured out how to reproduce it:
> > start nfsd with 50 instances and then try to stop it.
> 
> So, all it takes is this?:
> 
> 	rpc.nfsd 50
> 	rpc.nfsd 0

I guess so: On debian etch I adapted /etc/defaults/nfs-kernel-server
(IIRC) to start 50 daemons and after a reboot it sufficed to type
/etc/init.d/nfs-kernel-server stop to make it say BUG. Very reproducable
here (5 machines).


> 
> > 
> > Jul  3 09:10:39 kernel: BUG: unable to handle kernel paging request at virtual address 6b6b6b6f
> > Jul  3 09:10:39 kernel:  printing eip:
> > Jul  3 09:10:39 kernel: c053f594
> > Jul  3 09:10:39 kernel: *pde = 00000000
> > Jul  3 09:10:39 kernel: Oops: 0000 [#1]
> > Jul  3 09:10:39 kernel: SMP
> > Jul  3 09:10:39 kernel: Modules linked in: vmthrottle
> 
> What's vmthrottle, by the way?

That's a custom module to kill memory hungry processes when the uid
doesn't match the one running the X server (basically). That way 40-50
workstations for software development can also participate in distributed
compiler testing without interfering too much. An unpatched and moduleless
kernel still crashes.

> 
> > Jul  3 09:10:39 kernel: CPU:    1
> > Jul  3 09:10:39 kernel: EIP:    0060:[<c053f594>]    Not tainted VLI
> > Jul  3 09:10:39 kernel: EFLAGS: 00010202   (2.6.21.5-x160 #1)
> > Jul  3 09:10:39 kernel: EIP is at cache_clean+0x124/0x1e0
> > Jul  3 09:10:39 kernel: eax: 00000000   ebx: 6b6b6b6b   ecx: c06dffa0   edx: c0a1f380
> > Jul  3 09:10:39 kernel: esi: f672d800   edi: 00000000   ebp: f5a11f40   esp: f5a11f34
> > Jul  3 09:10:39 kernel: ds: 007b   es: 007b   fs: 00d8  gs: 0000  ss: 0068
> > Jul  3 09:10:39 kernel: Process nfsd (pid: 4420, ti=f5a10000 task=f596c070 task.ti=f5a10000)
> > Jul  3 09:10:39 kernel: Stack: c06dffa0 f6a3c268 f6a3c234 f5a11f48 c053f69f f5a11f54 c053f6da f6a3c260
> > Jul  3 09:10:39 kernel:        f5a11f5c c020ef47 f5a11f70 c0205632 c06597c8 f6a3c268 f6a3c7ac f5a11f94
> > Jul  3 09:10:39 kernel:        c0537b23 f59b2000 f5a11f94 00000286 f6a3c270 f59b2000 f6a3c7ac f6a3c234
> > Jul  3 09:10:39 kernel: Call Trace:
> > Jul  3 09:10:39 kernel:  [<c01054a9>] show_trace_log_lvl+0x19/0x30
> > Jul  3 09:10:39 kernel:  [<c010556b>] show_stack_log_lvl+0x8b/0xb0
> > Jul  3 09:10:39 kernel:  [<c01057c6>] show_registers+0x1e6/0x310
> > Jul  3 09:10:39 kernel:  [<c0105a4f>] die+0x10f/0x240
> > Jul  3 09:10:39 kernel:  [<c0115f82>] do_page_fault+0x342/0x610
> > Jul  3 09:10:39 kernel:  [<c054d1ac>] error_code+0x7c/0x90
> > Jul  3 09:10:39 kernel:  [<c053f69f>] cache_flush+0xf/0x30
> > Jul  3 09:10:39 kernel:  [<c053f6da>] cache_purge+0x1a/0x30
> > Jul  3 09:10:39 kernel:  [<c020ef47>] nfsd_export_flush+0x17/0x30
> 
> So I guess the nfsd export cache is corrupted somehow.
> 
> Perhaps turning on more debugging options in the kernel config would
> help catch the problem earlier.  I'm not having any luck reproducing
> this now.

Hmm, 6b6b6b6b looks like a poison to me and I have some debugging options on:

CONFIG_DEBUG_KERNEL=y
CONFIG_SLAB=y
CONFIG_DEBUG_SLAB=y
CONFIG_DETECT_SOFTLOCKUP=y
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_DEBUG_SPINLOCK_SLEEP=y
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_DEBUG_STACKOVERFLOW=y

Full config: http://www.frankvm.com/tmp/dot-config-cachebug


-- 
Frank

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