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Date: Thu, 3 Sep 2009 12:34:28 +0100
From: Nick Craig-Wood <nick@craig-wood.com>
To: linux-kernel@vger.kernel.org
Subject: Reading /proc/kcore causes a BUG()
Message-ID: <20090903113428.GA6986@craig-wood.com>
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Is a fix for this going to make 2.6.31?

To replicate

  cat /proc/kcore >/dev/null 

See also

  http://bugzilla.kernel.org/show_bug.cgi?id=13850

To get

BUG: unable to handle kernel paging request at eda08000
IP: [<c01a0e98>] read_kcore+0x27f/0x341
*pdpt = 0000000071809027
Oops: 0000 [#1] SMP
last sysfs file: /sys/class/net/lo/operstate

Pid: 2361, comm: cat Not tainted (2.6.31.git-x1 #1)
EIP: 0061:[<c01a0e98>] EFLAGS: 00010286 CPU: 1
EIP is at read_kcore+0x27f/0x341
EAX: c04404fc EBX: 00001000 ECX: 00000400 EDX: eda09000
ESI: eda08000 EDI: ec129000 EBP: ec60bf48 ESP: ec60bf10
 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0069
Process cat (pid: 2361, ti=ec60a000 task=ecf800b0 task.ti=ec60a000)
Stack:
 00001000 08051000 00000000 00001000 00000003 eda08000 ec129000 c04404fc
<0> eda09000 00000000 00001000 ecd39380 fffffffb c01a0c19 ec60bf6c c019a907
<0> ec60bf98 00001000 08051000 eccbab00 eccbab00 c019a8af 00001000 ec60bf8c
Call Trace:
 [<c01a0c19>] ? read_kcore+0x0/0x341
 [<c019a907>] ? proc_reg_read+0x58/0x6c
 [<c019a8af>] ? proc_reg_read+0x0/0x6c
 [<c016905e>] ? vfs_read+0x87/0x110
 [<c0169180>] ? sys_read+0x3b/0x60
 [<c0106a4d>] ? syscall_call+0x7/0xb
Code: d3 29 f3 89 f8 29 f0 39 d7 0f 46 d8 8d 0c 33 89 4d e8 29 5d ec 8b 45 e4 f6 40 0c 01 75 18 89 d9 c1 e9 02 89 f7 2b 7d dc 03 7d e0 <f3> a5 89 d9 83 e1 03 74 02 f3 a4 8b 55 e4 8b 12 89 55 e4 83 7d
EIP: [<c01a0e98>] read_kcore+0x27f/0x341 SS:ESP 0069:ec60bf10
CR2: 00000000eda08000
---[ end trace 4387f828fd1590eb ]---

I tried this on the latest git checkout (as of 2009-09-03 11:00 GMT)
under Xen as a domU.  The bugzilla report states it happens on non xen
machines also.

I know reading /proc/kcore isn't such a good idea, but badly written
backup scripts are triggering this on our customer's servers :-(

-- 
Nick Craig-Wood <nick@craig-wood.com> -- http://www.craig-wood.com/nick
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