Re: [PATCH] mm/oom: added option 'oom_dump_task_cmdline'

[Michal Hocko <mhocko@kernel.org>]

On Wed 20-02-19 09:37:56, Bujnak, Stepan wrote:
> On Wed, Feb 20, 2019 at 7:49 AM Michal Hocko <mhocko@kernel.org> wrote:
[...]
> > You are trying to allocate from the OOM context. That is a big no no.
> > Not to mention that this is deadlock prone because get_cmdline needs
> > mmap_sem and the allocating context migh hold the lock already. So the
> > patch is simply wrong.
> >
> 
> Thanks for the notes. I understand how allocating from OOM context
> is a problem. However I still believe that this would be helpful
> for debugging OOM kills since task->comm is often not descriptive
> enough. Would it help if instead of calling kstrdup_quotable_cmdline()
> which allocates the buffer on heap I called get_cmdline() directly
> passing it stack-allocated buffer of certain size e.g. 256?

No it wouldn't because get_cmdline take mmap_sem lock as already pointed
out.

Please also note that the cmd line might be considered security/privacy
sensitive information and dumping it to the log sounds like a bad idea
in general.
-- 
Michal Hocko
SUSE Labs