Re: exercising current aarch64 kprobe support with systemtap

[William Cohen <wcohen@redhat.com>]

On 08/03/2016 09:13 AM, Pratyush Anand wrote:
> On 07/07/2016:03:58:37 PM, Frank Ch. Eigler wrote:
>> David Long <dave.long@linaro.org> writes:
>>
>>> [...]
>>>> - bug_handler() calls report_bug() which calls __warn()
>>>> - __warn() does lot of pr_warn()  which invokes print_worker_info()
>>>> where we have a kprobe instrumented.
>>>> - Therefore, we are encountering this issue.
> 
> Hi Will,
> 
> Can you please cross-check if following branch works perfectly with
> kprobes_onthefly.exp and other systemtap tests.
> 
> https://github.com/pratyushanand/linux/tree/uprobe/upstream_arm64_devel_v1.1
> 
> Following patch in above branch should solve this issue.
> https://github.com/pratyushanand/linux/commit/d0dcc6477f1279ab0bd99aefc30efdecb16c586e
> 
> However, I am not yet sure that above modification could be the best solution,
> so discussing at arm kernel list.
> 
> ~Pratyush
> 

Hi Pratyush,

I am setting up a machine with the locally built kernel and systemtap to see if the problem is resolved. I hope to have some results by this evening.

Could there be a better way to handle the "Unexpected kernel single-step exception at EL1"?  Getting stuck in a loop endlessly quickly printing out that message isn't very helpful. Maybe use pr_warn_ratelimited instead of pr_warn.

-Will