Subject: Re: 2.6.31-git5 kernel boot hangs on powerpc

From: Sachin Sant <[email-masked]>
Date: Thu, 24 Sep 2009 18:53:09 +0530

Tejun Heo wrote:
> Sachin Sant wrote:
>   
>> Tejun Heo wrote:
>>     
>>> Can you please apply the attached patch and see whether anything
>>> interesting shows up in the kernel log?
>>>   
>>>       
>> Thanks Tejun for the debug patch. Attached here are the relevant logs.
>> The only messages related to percpu in the logs are
>>
>> <6>PERCPU: Embedded 2 pages/cpu @c000000001200000 s100232 r0 d30840 u524288
>> <7>pcpu-alloc: s100232 r0 d30840 u524288 alloc=1*1048576
>> <7>pcpu-alloc: [0] 0 1
>> The captured logs are with latest git.
>>     
>
> Hmm... that means it wasn't caused by rogue percpu pointer access.
> Pleast wait a bit.  I'll try to reproduce it.
>   
I was able to reproduce the hang in a different way. (I still had
IPV6 disabled in my config). I executed the network namespace container
tests from LTP and could reproduce a similar hang. The top three
function calls were the same as with IPV6. Here are the traces
using xmon debugger.

Oops: System Reset, sig: 6 [#4]
SMP NR_CPUS=1024 DEBUG_PAGEALLOC NUMA pSeries
Modules linked in: quota_v2 quota_tree fuse loop dm_mod sg sd_mod crc_t10dif ibmvscsic scsi_transport_srp scsi_tgt scsi_mod
NIP: c00000000003c310 LR: c0000000000055d0 CTR: 0000000000000040
REGS: c0000000fc90f340 TRAP: 0100   Tainted: G      D     (2.6.31-git13-autotest)
MSR: 8000000000081032 <ME,IR,DR>  CR: 28004420  XER: 20000001
TASK = c00000002c408890[8753] 'check_netns_ena' THREAD: c0000000fc90c000 CPU: 2
GPR00: 00000fffffffffff c0000000fc90f5c0 c000000000b8c2a8 d00007fffff00000
GPR04: 0000000000000201 0000000000000300 d00007fffff00000 d00007fffff00000
GPR08: 0000000000000000 000007fffff00000 0000000000000000 0000000000000000
GPR12: 8000000000009032 c000000000c82a00 0000000000000001 c0000000fc90f924
GPR16: 0000000000000300 0000000000000001 c0000000fa8e2380 0000000000000000
GPR20: 0000000000010000 0000000000000001 0000000000000000 0000000000000000
GPR24: c0000000fa9c09c8 0000000000000001 0000000000000001 c0000000faef6f60
GPR28: c000000000c6b620 0000000000000000 c000000000af2aa0 c000000000c6d1b0
NIP [c00000000003c310] .hash_page+0x24/0x4bc
LR [c0000000000055d0] .do_hash_page+0x50/0x6c
Call Trace:
[c0000000fc90f5c0] [c0000000000055d0] .do_hash_page+0x50/0x6c (unreliable)
--- Exception: 301 at .memset+0x60/0xfc
    LR = .pcpu_alloc+0x718/0x8fc
[c0000000fc90f8b0] [c0000000001700dc] .pcpu_alloc+0x6a8/0x8fc (unreliable)
[c0000000fc90f9d0] [c000000000614648] .snmp_mib_init+0x54/0x9c
[c0000000fc90fa60] [c000000000614764] .ipv4_mib_init_net+0xd4/0x1e0
[c0000000fc90fb10] [c0000000005a839c] .setup_net+0x68/0x124
[c0000000fc90fbb0] [c0000000005a8ad0] .copy_net_ns+0x88/0x130
[c0000000fc90fc40] [c0000000000bd5ac] .create_new_namespaces+0x110/0x1d0
[c0000000fc90fce0] [c0000000000bd874] .unshare_nsproxy_namespaces+0x6c/0xe8
[c0000000fc90fd80] [c000000000091ee8] .SyS_unshare+0x13c/0x318
[c0000000fc90fe30] [c0000000000085b4] syscall_exit+0x0/0x40
Instruction dump:
7c0803a6 ebe1fff8 4e800020 78690100 7c0802a6 f8010010 3800ffff fa01ff80
7cb02b78 78000500 fa21ff88 fb61ffd8 <7c912378> fa41ff90 7c7b1b78 fa61ff98

As you can see the call trace is same as far as top three function calls
are concerned [snmp_mib_init(), pcpu_alloc() and memset()].

The snmp_mib_init() function is :

int snmp_mib_init(void *ptr[2], size_t mibsize)
{
        BUG_ON(ptr == NULL);
        ptr[0] = __alloc_percpu(mibsize, __alignof__(unsigned long long));
        if (!ptr[0])
                goto err0;
        ptr[1] = __alloc_percpu(mibsize, __alignof__(unsigned long long));
        if (!ptr[1])
                goto err1;
        return 0;
.....

May be this might help..

Thanks
-Sachin

-- 

---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
---------------------------------