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SubjectISSUE: 2.1.37-pre2 - NULL pointer bug in shm_swap() code
Hi,

very PC:

[1.] 2.1.37-pre2 - NULL pointer bug in shm_swap() code

[2.] in the desperate hope to find a stable smp kernel we went to
2.1.37-pre2 which is rather stable as long as you use the newer tulip
drivers as a module instead of linking it to the kernel.
However as soon as it comes to swapping of shm the kernel oopses:

[3.] keywords: ipc/shm/swap

[4.]
Linux version 2.1.37 (root@kirk.desy.de) (gcc version 2.7.2.1) #9 Fri May 2 11:02:29 MET DST 1997

[5.]
Unable to handle kernel NULL pointer dereference at virtual address 00000030
current->tss.cr3 = 00101000, Lr3 = 00101000
*pde = 00000000
Oops: 0000
CPU: 1
EIP: 0010:[<c013d0dc>]
EFLAGS: 00010286
eax: 03b3e045 ebx: c7d29400 ecx: 40000000 edx: c3b0b000
esi: c00977d8 edi: 00000000 ebp: 40000000 esp: c000df78
ds: 0018 es: 0018 ss: 0018
Process kswapd (pid: 3, process nr: 4, stackpage=c000d000)
Stack: 00000006 00000000 00000003 00000000 00000000 40000000 c3b3e000 0000004b
00000000 00000000 00000000 00002b00 c00977d8 03b3e067 03b3e045 c0123e94
00000006 00000000 00000000 c01c86c0 c000c000 00009000 c01240c3 00000003
Call Trace:
Code: 8b 47 30 c1 e8 08 83 e0 7f 39 44 24 28 74 19 50 8b 74 24 2c

---

This translates to:

Using `/System.map' to map addresses to symbols.

>>EIP: c013d0dc <shm_swap+128/2fc>

Code: c013d0dc <shm_swap+128/2fc>

or in c-code:

ipc/shm.c: 758
if (shp->attaches)
for (shmd = shp->attaches; ; ) {
do {
pgd_t *page_dir;
pmd_t *page_middle;
pte_t *page_table, pte;
unsigned long tmp;

-*> if ((SWP_OFFSET(shmd->vm_pte) & SHM_ID_MASK) != id) {

obviously shmd = shp->attaches equals the NULL pointer and this is
not checked for.

[7.1]
Linux kirk.desy.de 2.1.37 #9 Fri May 2 11:02:29 MET DST 1997 i686 unknown
Kernel modules 2.1.34
Gnu C 2.7.2.1
Binutils 2.7.0.9
Linux C Library 5.4.23
Dynamic Linker (ld.so) 1.8.10
Linux C++ Library 27.1.0
Procps 0.99
Mount 2.6g
Net-tools 1.3.50-BETA6f
Kbd 0.93
Sh-utils 1.16

[7.2]
processor : 0
cpu : 686
model : Pentium Pro
vendor_id : GenuineIntel
stepping : 9
fdiv_bug : no
hlt_bug : no
fpu : yes
fpu_exception : yes
cpuid : yes
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic 11 mtrr pge mca cmov
bogomips : 199.07

processor : 1
cpu : 686
model : Pentium Pro
vendor_id : GenuineIntel
stepping : 9
fdiv_bug : no
hlt_bug : no
fpu : yes
fpu_exception : yes
cpuid : yes
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic 11 mtrr pge mca cmov
bogomips : 199.07

[7.3.]
$ cat /proc/modules
tulip 17672 1 (autoclean)

[7.4.] SCSI information (from /proc/scsi/scsi):

Doescat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: Model: DFRSS4F Rev: 4B4B
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
Vendor: Model: DFRSS4F Rev: 4B4B
Type: Direct-Access ANSI SCSI revision: 02


[7.5]
cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 130707456 119865344 10842112 13778944 86577152 15613952
Swap: 132567040 0 132567040
MemTotal: 127644 kB
MemFree: 10588 kB
MemShared: 13456 kB
Buffers: 84548 kB
Cached: 15248 kB
SwapTotal: 129460 kB
SwapFree: 129460 kB

[99.]
anyone have a qualified fix? ;-)

Wolfgang

--
_/ _/ _/ _/ _/_/_/ . Wolfgang Wander HERMES Collaboration
_/ _/ _/ _/ _/ . DESY Hamburg Email: Wolfgang.Wander@desy.de
_/_/_/ _/_/_/ _/ . Notkestr. 85 Tel: +49 40 8998 4638 Fax: -4034
_/_/_/ _/_/_/ _/_/_/ . 22603 Hamburg http://www-hermes.desy.de/wander.html

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