Re: [PATCH v5 09/10] Uprobes/sdt: Document about reference counter

[Ravi Bangoria]

Hi Srikar,

On 07/02/2018 08:24 PM, Srikar Dronamraju wrote:
> * Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx> [2018-06-28 10:52:08]:
> 
>> Reference counter gate the invocation of probe. If present,
>> by default reference count is 0. Kernel needs to increment
>> it before tracing the probe and decrement it when done. This
>> is identical to semaphore in Userspace Statically Defined
>> Tracepoints (USDT).
>>
>> Document usage of reference counter.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
>> Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> 
> Unlike perf, this mechanism cannot detect ref count and depends on the
> users data. What happens if the user mistakenly provides a wrong location?
> I guess he can corrupt some other data structures?

Yes, if user is giving wrong ref_ctr_offset, uprobe infrastructure will
corrupt some user data.

> 
> Hence I would think twice of advertising this mechanism. i.e keep this
> as an undocumented feature.
> 

I don't mind.

Thanks,
Ravi