Re: + c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-update-after-mm-num_exe_file_vmas-removal.patch added to -mm tree

From: Konstantin Khlebnikov
Date: Thu Apr 19 2012 - 18:28:31 EST

Oleg Nesterov wrote:
On 04/20, Cyrill Gorcunov wrote:

Guys, while I more-less agree with Matt about single-shot behaviour

[ let me copy my and his email

>> With mm->exe_file this prctl option become a one-shot
>> only, and while at moment our user-space tool can perfectly
>> live with that I thought that there is no strict need to
>> limit the option this way from the very beginning.
> As far as backward compatibility, isn't it better to lift that restriction
> later rather than add it? I think the latter would very likely "break"
> things whereas the former would not.
> I also prefer that restriction because it establishes a bound on how
> frequently the symlink can change. Keeping it a one-shot deal makes the
> values that show up in tools like top more reliable for admins.

I guess maybe it's time to drop one-shot requirement and as result
we can drop MMF_EXE_FILE_CHANGED bit completely,

Plus perhaps we can remove this for_each_vma check?

making overall code

Personally I'd certainly prefer this ;)

But let me repeat to avoid the confusion. I am fine either way,
I am not going to discuss this again unless I see something which
looks technically wrong. And the current MMF_EXE_FILE_CHANGED
doesn't look right even if the problem is minor.

Yeah, whole this protection does not protect anything and can be easily bypassed.
For example task can re-execute itself and change exe-file again and again.


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