Re: exercising current aarch64 kprobe support with systemtap

[David Long <dave.long@linaro.org>]

On 08/03/2016 10:51 AM, William Cohen wrote:
> 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
>

Just a reminder that the latest kprobes patches are on the end of the 
for-next/kprobes branch in the:

git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git

repo.  There's at least one more tweak to that (removing jprobe stack 
copy) coming up shortly.

Thanks,
-dl