OpenVZ developers team has encountered the following problem in 2.6.19-rc6
kernel. After some seconds of running script
while [[ 1 ]]
do
find /proc -name mountstats | xargs cat
done
this Oops appears:
BUG: unable to handle kernel NULL pointer dereference at virtual address
00000010
printing eip:
c01a6b70
*pde = 00000000
Oops: 0000 [#1]
SMP
Modules linked in: xt_length ipt_ttl xt_tcpmss ipt_TCPMSS iptable_mangle
iptable_filter xt_multiport xt_limit ipt_tos ipt_REJECT ip_tables x_tables
parport_pc lp parport sunrpc af_packet thermal processor fan button battery
asus_acpi ac ohci_hcd ehci_hcd usbcore i2c_nforce2 i2c_core tg3 floppy
pata_amd
ide_cd cdrom sata_nv libata
CPU: 1
EIP: 0060:[<c01a6b70>] Not tainted VLI
EFLAGS: 00010246 (2.6.19-rc6 #2)
EIP is at mountstats_open+0x70/0xf0
eax: 00000000 ebx: e6247030 ecx: e62470f8 edx: 00000000
esi: 00000000 edi: c01a6b00 ebp: c33b83c0 esp: f4105eb4
ds: 007b es: 007b ss: 0068
Process cat (pid: 6044, ti=f4105000 task=f4104a70 task.ti=f4105000)
Stack: c33b83c0 c04ee940 f46a4a80 c33b83c0 e4df31b4 c01a6b00 f4105000 c0169231
e4df31b4 c33b83c0 c33b83c0 f4105f20 00000003 f4105000 c0169445 f2503cf0
f7f8c4c0 00008000 c33b83c0 00000000 00008000 c0169350 f4105f20 00008000
Call Trace:
[<c01a6b00>] mountstats_open+0x0/0xf0
[<c0169231>] __dentry_open+0x181/0x250
[<c0169445>] nameidata_to_filp+0x35/0x50
[<c0169350>] do_filp_open+0x50/0x60
[<c01873d6>] seq_read+0xc6/0x300
[<c0169511>] get_unused_fd+0x31/0xc0
[<c01696d3>] do_sys_open+0x63/0x110
[<c01697a7>] sys_open+0x27/0x30
[<c01030bd>] sysenter_past_esp+0x56/0x79
=======================
Code: 45 74 8b 54 24 20 89 44 24 08 8b 42 f0 31 d2 e8 47 cb f8 ff 85 c0 89 c3
74 51 8d 80 a0 04 00 00 e8 46 06 2c 00 8b 83 48 04 00 00 <8b> 78 10 85 ff 74
03
f0 ff 07 b0 01 86 83 a0 04 00 00 f0 ff 4b
EIP: [<c01a6b70>] mountstats_open+0x70/0xf0 SS:ESP 0068:f4105eb4
The problem is that task->nsproxy can be equal NULL for some time during
task exit. This patch fixes the BUG.
Signed-off-by: Vasily Tarasov <[email protected]>
--
--- ./fs/proc/base.c.mountstatsfix 2006-11-18 02:43:48.000000000 +0300
+++ ./fs/proc/base.c 2006-11-18 03:11:41.000000000 +0300
@@ -442,7 +442,8 @@
if (task) {
task_lock(task);
- namespace = task->nsproxy->namespace;
+ if (task->nsproxy)
+ namespace = task->nsproxy->namespace;
if (namespace)
get_namespace(namespace);
task_unlock(task);
--- ./include/linux/nsproxy.h.mountstatsfix 2006-11-18 02:43:51.000000000 +0300
+++ ./include/linux/nsproxy.h 2006-11-18 03:15:25.000000000 +0300
@@ -45,8 +45,10 @@
{
struct nsproxy *ns = p->nsproxy;
if (ns) {
- put_nsproxy(ns);
+ task_lock(p);
p->nsproxy = NULL;
+ task_unlock(p);
+ put_nsproxy(ns);
}
}
#endif
Quoting Vasily Tarasov ([email protected]):
> OpenVZ developers team has encountered the following problem in 2.6.19-rc6
> kernel. After some seconds of running script
>
> while [[ 1 ]]
> do
> find /proc -name mountstats | xargs cat
> done
>
> this Oops appears:
>
> BUG: unable to handle kernel NULL pointer dereference at virtual address
> 00000010
> printing eip:
> c01a6b70
> *pde = 00000000
> Oops: 0000 [#1]
> SMP
> Modules linked in: xt_length ipt_ttl xt_tcpmss ipt_TCPMSS iptable_mangle
> iptable_filter xt_multiport xt_limit ipt_tos ipt_REJECT ip_tables x_tables
> parport_pc lp parport sunrpc af_packet thermal processor fan button battery
> asus_acpi ac ohci_hcd ehci_hcd usbcore i2c_nforce2 i2c_core tg3 floppy
> pata_amd
> ide_cd cdrom sata_nv libata
> CPU: 1
> EIP: 0060:[<c01a6b70>] Not tainted VLI
> EFLAGS: 00010246 (2.6.19-rc6 #2)
> EIP is at mountstats_open+0x70/0xf0
> eax: 00000000 ebx: e6247030 ecx: e62470f8 edx: 00000000
> esi: 00000000 edi: c01a6b00 ebp: c33b83c0 esp: f4105eb4
> ds: 007b es: 007b ss: 0068
> Process cat (pid: 6044, ti=f4105000 task=f4104a70 task.ti=f4105000)
> Stack: c33b83c0 c04ee940 f46a4a80 c33b83c0 e4df31b4 c01a6b00 f4105000 c0169231
> e4df31b4 c33b83c0 c33b83c0 f4105f20 00000003 f4105000 c0169445 f2503cf0
> f7f8c4c0 00008000 c33b83c0 00000000 00008000 c0169350 f4105f20 00008000
> Call Trace:
> [<c01a6b00>] mountstats_open+0x0/0xf0
> [<c0169231>] __dentry_open+0x181/0x250
> [<c0169445>] nameidata_to_filp+0x35/0x50
> [<c0169350>] do_filp_open+0x50/0x60
> [<c01873d6>] seq_read+0xc6/0x300
> [<c0169511>] get_unused_fd+0x31/0xc0
> [<c01696d3>] do_sys_open+0x63/0x110
> [<c01697a7>] sys_open+0x27/0x30
> [<c01030bd>] sysenter_past_esp+0x56/0x79
> =======================
> Code: 45 74 8b 54 24 20 89 44 24 08 8b 42 f0 31 d2 e8 47 cb f8 ff 85 c0 89 c3
> 74 51 8d 80 a0 04 00 00 e8 46 06 2c 00 8b 83 48 04 00 00 <8b> 78 10 85 ff 74
> 03
> f0 ff 07 b0 01 86 83 a0 04 00 00 f0 ff 4b
> EIP: [<c01a6b70>] mountstats_open+0x70/0xf0 SS:ESP 0068:f4105eb4
>
> The problem is that task->nsproxy can be equal NULL for some time during
> task exit. This patch fixes the BUG.
>
> Signed-off-by: Vasily Tarasov <[email protected]>
Thanks, Vasily. I couldn't reproduce the bug, but I see it must be
there. Fix looks good, and boots and tests fine here.
Acked-by: Serge E. Hallyn <[email protected]>
> --
>
> --- ./fs/proc/base.c.mountstatsfix 2006-11-18 02:43:48.000000000 +0300
> +++ ./fs/proc/base.c 2006-11-18 03:11:41.000000000 +0300
> @@ -442,7 +442,8 @@
>
> if (task) {
> task_lock(task);
> - namespace = task->nsproxy->namespace;
> + if (task->nsproxy)
> + namespace = task->nsproxy->namespace;
> if (namespace)
> get_namespace(namespace);
> task_unlock(task);
> --- ./include/linux/nsproxy.h.mountstatsfix 2006-11-18 02:43:51.000000000 +0300
> +++ ./include/linux/nsproxy.h 2006-11-18 03:15:25.000000000 +0300
> @@ -45,8 +45,10 @@
> {
> struct nsproxy *ns = p->nsproxy;
> if (ns) {
> - put_nsproxy(ns);
> + task_lock(p);
> p->nsproxy = NULL;
> + task_unlock(p);
> + put_nsproxy(ns);
> }
> }
> #endif
> -
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