Re: r212281 breaks KDE

On Sun, Sep 12, 2010 at 10:42:57AM -0400, Michael Butler wrote:
> For the last week, on and off, I've been looking for something that
> caused KDE to be horridly unstable, i.e. machine freezes with and
> without a core-dump.
> 
> Removing r212281 (and r212282) restores that stability. Is there a race
> condition that this update exposes by reducing lock strength?
> 
> The most common failure with this code included produces a back-trace
> similar to the one attached,
> 
> 	imb

> toshi.auburn.protected-networks.net dumped core - see /var/crash/vmcore.0
> 
> Sat Sep 11 15:33:22 EDT 2010
> 
> FreeBSD toshi.auburn.protected-networks.net 9.0-CURRENT FreeBSD 9.0-CURRENT #5 r212466M: Sat Sep 11 10:10:59 EDT 2010     root_at_toshi.auburn.protected-networks.net:/usr/obj/usr/home/imb/svn/head/sys/TOSHI  i386
> 
> panic: page fault
> 
> GNU gdb 6.1.1 [FreeBSD]
> Copyright 2004 Free Software Foundation, Inc.
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> Type "show copying" to see the conditions.
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> This GDB was configured as "i386-marcel-freebsd"...
> 
> Unread portion of the kernel message buffer:
> 
> 
> Fatal trap 12: page fault while in kernel mode
> cpuid = 0; apic id = 00
> fault virtual address	= 0x22c
> fault code		= supervisor read, page not present
> instruction pointer	= 0x20:0xc066705a
> stack pointer	        = 0x28:0xe944b7f8
> frame pointer	        = 0x28:0xe944b810
> code segment		= base 0x0, limit 0xfffff, type 0x1b
> 			= DPL 0, pres 1, def32 1, gran 1
> processor eflags	= interrupt enabled, resume, IOPL = 0
> current process		= 1938 (kdeinit4)
> trap number		= 12
> panic: page fault
> cpuid = 0
> Uptime: 2m33s
> Physical memory: 3049 MB
> Dumping 225 MB: 210 194 178 162 146 130 114 98 82 66 50 34 18 2
> 
> Reading symbols from /boot/modules/vboxdrv.ko...done.
> Loaded symbols for /boot/modules/vboxdrv.ko
> Reading symbols from /boot/modules/vboxnetflt.ko...done.
> Loaded symbols for /boot/modules/vboxnetflt.ko
> Reading symbols from /boot/modules/vboxnetadp.ko...done.
> Loaded symbols for /boot/modules/vboxnetadp.ko
> Reading symbols from /usr/local/modules/fuse.ko...done.
> Loaded symbols for /usr/local/modules/fuse.ko
> #0  doadump () at pcpu.h:231
> 231	pcpu.h: No such file or directory.
> 	in pcpu.h
> (kgdb) #0  doadump () at pcpu.h:231
> #1  0xc06760f7 in boot (howto=260)
>     at /usr/home/imb/svn/head/sys/kern/kern_shutdown.c:416
> #2  0xc06764e8 in panic (fmt=0x104 <Address 0x104 out of bounds>)
>     at /usr/home/imb/svn/head/sys/kern/kern_shutdown.c:590
> #3  0xc09950ff in trap_fatal (frame=0xe944b7b8, eva=40)
>     at /usr/home/imb/svn/head/sys/i386/i386/trap.c:980
> #4  0xc0995469 in trap_pfault (frame=0xe944b7b8, usermode=0, eva=556)
>     at /usr/home/imb/svn/head/sys/i386/i386/trap.c:893
> #5  0xc09958f7 in trap (frame=0xe944b7b8)
>     at /usr/home/imb/svn/head/sys/i386/i386/trap.c:568
> #6  0xc097e16c in calltrap ()
>     at /usr/home/imb/svn/head/sys/i386/i386/exception.s:168
> #7  0xc066705a in _mtx_lock_sleep (m=0xc81c26e8, tid=3343885696, opts=0, 
>     file=0x0, line=0) at /usr/home/imb/svn/head/sys/kern/kern_mutex.c:369
> #8  0xc09385d8 in vnode_create_vobject (vp=0xc825a330, isize=512, 
>     td=0xc74fa580) at /usr/home/imb/svn/head/sys/vm/vnode_pager.c:111
From the frame 8, please print the content of the *vp, and from it,
content of vm object. The corresponding kgdb commands would be
frame 8
p *vp
p *(vp->v_bufobj.bo_object)