Date:	Wed, 29 Jul 2009 08:48:25 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	scgtrp@...il.com, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org,
	Amerigo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Bugme-new] [Bug 13850] New: reading /proc/kcore causes oops

On Tue, 28 Jul 2009 16:05:27 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> 
> (switched to email.  Please respond via emailed reply-to-all, not via the
> bugzilla web interface).
> 
> On Mon, 27 Jul 2009 03:19:11 GMT
> bugzilla-daemon@...zilla.kernel.org wrote:
> 
> > http://bugzilla.kernel.org/show_bug.cgi?id=13850
> > 
> >            Summary: reading /proc/kcore causes oops
> >            Product: Other
> >            Version: 2.5
> >     Kernel Version: 2.6.30
> >           Platform: All
> >         OS/Version: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: Other
> >         AssignedTo: other_other@...nel-bugs.osdl.org
> >         ReportedBy: scgtrp@...il.com
> >         Regression: No
> > 
> > 
> > When trying to use an old trick for finding lost data by grep'ing /proc/kcore,
> > I managed to oops my server's kernel. I tried again on my desktop with cat
> > /proc/kcore >/dev/null. cat was killed, and a similar oops appeared in my dmesg
> > which I managed to capture:
> > 
> > Jul 26 23:04:13 mike kernel: BUG: unable to handle kernel paging request at
> > e07cf000
> > Jul 26 23:04:13 mike kernel: IP: [<c0224dd1>] read_kcore+0x2c1/0x4b0
> > Jul 26 23:04:13 mike kernel: *pde = 1b5f4067 *pte = 00000000 
> > Jul 26 23:04:13 mike kernel: Oops: 0000 [#2] PREEMPT SMP 
> > Jul 26 23:04:13 mike kernel: last sysfs file: /sys/power/state
> > Jul 26 23:04:13 mike kernel: Modules linked in: ipv6 sg sd_mod fuse usb_storage
> > usbhid hid snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device
> > snd_pcm_oss snd_mixer_oss ppdev snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm
> > snd_timer ohci_hcd parport_pc lp parport snd soundcore snd_page_alloc nvidia(P)
> > agpgart k8temp ehci_hcd forcedeth i2c_nforce2 i2c_core usbcore evdev thermal
> > processor fan button battery ac rtc_cmos rtc_core rtc_lib ext3 jbd mbcache
> > ide_gd_mod ide_cd_mod cdrom sata_nv libata amd74xx ide_pci_generic ide_core
> > scsi_mod
> > Jul 26 23:04:13 mike kernel: 
> > Jul 26 23:04:13 mike kernel: Pid: 4835, comm: cat Tainted: P      D   
> > (2.6.30-ARCH #1) W3107
> > Jul 26 23:04:13 mike kernel: EIP: 0060:[<c0224dd1>] EFLAGS: 00210286 CPU: 0
> > Jul 26 23:04:13 mike kernel: EIP is at read_kcore+0x2c1/0x4b0
> > Jul 26 23:04:13 mike kernel: EAX: ddb71ac0 EBX: 00001000 ECX: 00000400 EDX:
> > e07d0000
> > Jul 26 23:04:13 mike kernel: ESI: e07cf000 EDI: da20e000 EBP: d73fbf30 ESP:
> > d73fbefc
> > Jul 26 23:04:13 mike kernel: DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
> > Jul 26 23:04:13 mike kernel: Process cat (pid: 4835, ti=d73fa000 task=d4b5cc00
> > task.ti=d73fa000)
> > Jul 26 23:04:13 mike kernel: Stack:
> > Jul 26 23:04:13 mike kernel: da20e000 e07cf000 d73fbf90 00000000 09459000
> > 00000000 00008000 00001000
> > Jul 26 23:04:13 mike kernel: 00000000 6798ed89 ddaf0000 ce920c80 c0224b10
> > fffffffb c0219e89 d73fbf90
> > Jul 26 23:04:13 mike kernel: 09459000 00008000 d73fbf90 6798ed89 ce920c80
> > 00008000 09459000 d73fbf80
> > Jul 26 23:04:13 mike kernel: Call Trace:
> > Jul 26 23:04:13 mike kernel: [<c0224b10>] ? read_kcore+0x0/0x4b0
> > Jul 26 23:04:13 mike kernel: [<c0219e89>] ? proc_reg_read+0x79/0xc0
> > Jul 26 23:04:13 mike kernel: [<c01d1b43>] ? vfs_read+0xc3/0x1a0
> > Jul 26 23:04:13 mike kernel: [<c0219e10>] ? proc_reg_read+0x0/0xc0
> > Jul 26 23:04:13 mike kernel: [<c01d1d28>] ? sys_read+0x58/0xb0
> > Jul 26 23:04:13 mike kernel: [<c0103c73>] ? sysenter_do_call+0x12/0x28
> > Jul 26 23:04:13 mike kernel: Code: 89 fb 0f 43 f2 89 ca 29 f2 29 f3 39 f9 0f 46
> > da 29 5c 24 14 f6 40 0c 01 8d 14 33 75 19 89 d9 89 f7 c1 e9 02 2b 7c 24 04 03
> > 3c 24 <f3> a5 89 d9 83 e1 03 74 02 f3 a4 8b 4c 24 14 8b 00 85 c9 74 0a 
> > Jul 26 23:04:13 mike kernel: EIP: [<c0224dd1>] read_kcore+0x2c1/0x4b0 SS:ESP
> > 0068:d73fbefc
> > Jul 26 23:04:13 mike kernel: CR2: 00000000e07cf000
> > Jul 26 23:04:13 mike kernel: ---[ end trace 3bb140bf57c1987e ]---
> > Jul 26 23:04:13 mike kernel: note: cat[4835] exited with preempt_count 1
> > 
> > I understand it's quite a ridiculous thing to do, but userspace shouldn't be
> > able to cause kernel errors, no matter what kind of insane things I try.
> > 
> 
> gee, read_kcore() is huge.  This makes it pretty hard to work out where
> exactly the kernel died.
> 
> Is it reproducible, or do you still have the vmlinux from the above
> oops on-disk?
> 
> If so, can you please help work out where it crashed?  You could run
> something like
> 
> 	addr2line -e vmlinux 0xc0224dd1
> 
> or
> 
> 	gdb vmlinux
> 	(gdb) l *0xc0224dd1
> 
yes, disassemble will be helpful.
If you compiled the kernel by yourself, 
# objdump -d fs/proc/kcore.o

will also help us.

Hmm, but this message is curious.

unable to handle kernel paging request at e07cf000

What's layout of memory does your server have ? Could you show
# grep "System RAM" /proc/iomem
or head of dmesg ?

IIUC, current code doesn't assume any memory hole in direct-map area.
(And my new patch series should handle it even in CONFIG_HIGHMEM case.)

Thanks,
-Kame



> both of these will need CONFIG_DEBUG_INFO=y.
> 
> 
> It is possible to work out where the kernel crashed using the above
> Code: line, but it's a bit of a pain.
> 
> Thanks.
> 
> 

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