linux-kernel - Re: [External] Re: [RFC] mm: add new syscall pidfd_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y0avztF7QU8P/OoB@dhcp22.suse.cz>
Date:   Wed, 12 Oct 2022 14:15:10 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Zhongkun He <hezhongkun.hzk@...edance.com>
Cc:     corbet@....net, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, wuyun.abel@...edance.com
Subject: Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy()

On Wed 12-10-22 19:22:21, Zhongkun He wrote:
> > 
> > Yes, this will require some refactoring and one potential way is to make
> > mpol ref counting unconditional. The conditional ref. counting has
> > already caused issues in the past and the code is rather hard to follow
> > anyway. I am not really sure this optimization is worth it.
> > 
> > Another option would be to block the pidfd side of things on completion
> > which would wake it up from the task_work context but I would rather
> > explore the ref counting approach first and only if this is proven to be
> > too expensive to go with hacks like this.
> 
> Hi Michal
> 
> The counting approach means executing mpol_get/put() when start/finish using
> mempolicy,right?

We already do that via mpol_{get,put} but there are cases where the
reference counting is ignored because it cannot be freed and also mpol_cond_put
resp. open coded versions of mpol_needs_cond_ref.
-- 
Michal Hocko
SUSE Labs