Ooops with 2.6.39.2 on pxa270

[Russell King - ARM Linux]

On Mon, Jul 04, 2011 at 09:58:05PM +0300, Vasily Khoruzhick wrote:
> Hi there, I'm getting following oops on my device (Zipit Z2 with PXA270)
> with 2.6.39.2. And I have no idea what can be wrong :( Ooops is not 100% 
> reproducible, it happens in 50% of cases.

Short answer is I can't say for certain.  My compiler produces the
following for get_task_pid:

00000248 <get_task_pid>:
 248:   e1a0c00d        mov     ip, sp
 24c:   e92dd800        push    {fp, ip, lr, pc}
 250:   e24cb004        sub     fp, ip, #4      ; 0x4
 254:   e3510000        cmp     r1, #0  ; 0x0
 258:   159000e8        ldrne   r0, [r0, #232]
 25c:   e3a0300c        mov     r3, #12 ; 0xc
 260:   e0230391        mla     r3, r1, r3, r0
 264:   e5930104        ldr     r0, [r3, #260]
 268:   e3500000        cmp     r0, #0  ; 0x0

 26c:   0a000006        beq     28c <get_task_pid+0x44>
 270:   e10f2000        mrs     r2, CPSR
 274:   e3823080        orr     r3, r2, #128    ; 0x80
 278:   e121f003        msr     CPSR_c, r3
 27c:   e5903000        ldr     r3, [r0]		 <== faulting insn

 280:   e2833001        add     r3, r3, #1      ; 0x1
 284:   e5803000        str     r3, [r0]
 288:   e121f002        msr     CPSR_c, r2
 28c:   e89da800        ldm     sp, {fp, sp, pc}

which is close enough to your code line (except my r3 is your r1).

We know that the passed r1 value was PIDTYPE_PID, wihch means the ldrne
wasn't executed.

My first guess is that something has overwritten task->pids - either
memory corruption, memory wrap-around due to the kernel thinking it has
more memory than physically fitted, or a buggy driver stamping over
memory it shouldn't.