Re: sparc: deadlock using perf with sched tracepoints and user callstacks

[David Ahern <david.ahern@oracle.com>]

On 4/22/15 5:22 PM, David Miller wrote:
> From: David Ahern <david.ahern@oracle.com>
> Date: Tue, 31 Mar 2015 17:52:53 -0600
>
>> On 3/31/15 5:38 PM, David Miller wrote:
>>> What is different in the PowerPC fault path vs. the Sparc one that
>>> causes the SIGBUS for sparc where the PowerPC does not see it?
>>>
>>> I don't understand where the SIGBUS comes from.  In a pagefault
>>> disable section on sparc, in_atomic() should be true, thus we'll call
>>> do_kernel_fault(), fall through to the TSTATE_PRIV code path and
>>> simply run the exception handler.
>>>
>>
>> That's what I was hoping someone could explain to me. I'll dig deeper
>> on Monday.
>
> I've looked a few times at this and can't figure out what might be
> going wrong just from visual inspection.  I'll try reproducing the
> problem and adding some diagnostics.
>

All you need is 'perf sched record -g -- make -j 256'

gcc related tasks will start erroring out. Odd that it is mainly gcc and 
friends getting hit.

I threw a printk into all of the sigbus places under arch/sparc. One 
that kept triggering is sun4v_do_mna. I was not able to get any info 
about why.