debug problems on ppc 83xx target due to changed struct task_struct
benh at kernel.crashing.org
Wed Aug 17 08:13:52 AEST 2016
On Mon, 2016-08-15 at 09:19 -0700, Dave Hansen wrote:
> Wow, thanks for all the debugging here!
Yup, thanks, that's really odd... I wonder if one of those
structures is accessed beyond it's boundary, either the sigset
or the thread struct, causing corruption of neighbouring fields
in task struct...
Can you try adding a little canary on both sides (make it not-so-little
maybe a few words) which you initialize to a known pattern and check
every now and then ?
> So, we know it has to do with signals, thread_info, and probably only
> affects 32-bit powerpc. Seems awfully weird. Have you checked with
> of the 64-bit powerpc guys to see if they have any ideas?
> I went grepping around for a bit.
> Where is the task_struct stored? Is it on-stack on ppc32 or
No it's allocated normally.
> The thread_info is,
Yes, thread_info is at the bottom of stack
> I assume, but I see some THREAD_INFO vs. THREAD
> (thread struct) math happening in here, which confuses me:
> .globl ret_from_debug_exc
> mfspr r9,SPRN_SPRG_THREAD
> lwz r10,SAVED_KSP_LIMIT(r1)
> stw r10,KSP_LIMIT(r9)
> lwz r9,THREAD_INFO-THREAD(r9)
This calculates the offset between the thread struct and the pointer
to thread info inside task struct and loads that pointer into r9
> CURRENT_THREAD_INFO(r10, r1)
> lwz r10,TI_PREEMPT(r10)
> stw r10,TI_PREEMPT(r9)
> RET_FROM_EXC_LEVEL(SPRN_DSRR0, SPRN_DSRR1, PPC_RFDI)
Basically the above code transfers TI_PREEMPT from the "current"
thread info which I believe would be on some exception/interrupt
stack into the current task thread info.
> But, I'm really at a loss to explain this. It still seems like a
> ppc-specific issue. We can obviously work around it with an #ifdef
> your platform, but that's awfully hackish and hides the real bug,
> whatever it is.
> My suspicion is that there's a bug in the 32-bit ppc assembly
> I don't see any references to 'blocked' or 'real_blocked' in
> though. You could add a bunch of padding instead of moving the
> thread_struct and see if that does anything, but that's really a stab
> the dark.
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