Re: jffs2, 2.6.28-git8 : Weird problem.

[Jonathan Cameron <jic23@cam.ac.uk>]

Jonathan Cameron wrote:
> 
> 
>> Jonathan Cameron wrote:
>>> Having applied a few board specific patches on top of
>>> Linus' tree (around 2.6.28-git8)
>>> run into the following.
>>>
>>> Anyone have an ideas or seeing anything similar?
>> Yes, I think the same thing just happened on my avr32 board
>> (ATSTK1006)...see below.
>>
>>> Works fine on 2.6.28 so git bisection underway, but
>>> will take a while given speed of flashing this device
>>> (intelmote 2)
>> Please let me know the result, or if you need any help.
>>
>> Haavard
>>
>> Unable to handle kernel NULL pointer dereference at virtual address 00000150
>> ptbr = 93a9b000 pgd = 93b45000
>> Oops: Kernel access of bad area, sig: 11 [#1]
>> FRAME_POINTER chip: 0x01f:0x1e82 rev 2
>> Modules linked in:
>> PC is at set_dumpable+0x16/0x5e
>> LR is at commit_creds+0x86/0x10c
>> pc : [<9005bfc6>]    lr : [<9002e4fe>]    Not tainted
>> sp : 93bbff00  r12: 00000000  r11: 00000000
>> r10: ffffffff  r9 : 00000000  r8 : 00000150
>> r7 : 93bbff00  r6 : 939b9420  r5 : 901eca58  r4 : 00000000
>> r3 : 939e02e0  r2 : 90021494  r1 : 900a40c4  r0 : 93b52400
>> Flags: qvnzC
>> Mode bits: hjmde....G
>> CPU Mode: Supervisor
>> Process: jffs2_gcd_mtd1 [281] (task: 939e02e0 thread: 93bbe000)
>> Stack: (0x93bbff00 to 0x93bc0000)
>> ff00: 9002e4fe 93bbff14 939b9420 901eca58 00000000 90021b00 93bbff44 93bbe000 
>> ff20: 901ea8b0 00000000 00000000 90021494 900a40c4 93b52400 ffffffff ffffffff 
>> ff40: 93bbff58 900a40da 93bbffdc 00000000 93b52400 00000000 00000001 038e300c 
>> ff60: b3ec22cd 11c4148c b11833cc 338d19ec 77ca338c 734831ec 23dc63cc 33ec334c 
>> ff80: 33cc33cd 338c30cc 37cc338c b3fcb68d 9001be6c 93bbffa4 90204640 939e05c0 
>> ffa0: 93b5248c 90014166 93badcfc 90204640 939e05c0 93b5248c 00400000 900180e0 
>> ffc0: 900180e0 93bc0000 00000000 00000000 00000000 00000000 00000000 90021494 
>> ffe0: 00000000 00000000 00000000 00000000 00000000 90021494 900a40c4 93b52400 
>> Call trace:
>>  [<9002e4fe>] commit_creds+0x86/0x10c
>>  [<90021b00>] daemonize+0x14c/0x16c
>>  [<900a40da>] jffs2_garbage_collect_thread+0x16/0x108
>>  [<90021494>] do_exit+0x0/0x488
>>
> Hi All, 
> 
> Results of git bisection are in.  The patch highlighted as
> causing the problem is:
> 
> d84f4f992cbd76e8f39c488cf0c5d123843923b1 is first bad commit                              
> commit d84f4f992cbd76e8f39c488cf0c5d123843923b1                                           
> Author: David Howells <dhowells@redhat.com>                                               
> Date:   Fri Nov 14 10:39:23 2008 +1100                                                    
> 
>     CRED: Inaugurate COW credentials
>                                     
> ( lots of info ).
> 
> So now for the remaining question of why?
> 
Got to run in a mo, so thought I'd post my progress on 
working out what is happening.

For some reason, when set_dumpable is run in commit_creds
(cred.c) task->mm is null.  Don't know my way around
this bit of the kernel, but guessing that isn't good!