linux-kernel - Re: [RFC][PATCH] cgroup: Don't mess with tasks in exec

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Message-ID: <20180510123541.GO2368884@devbig577.frc2.facebook.com>
Date:   Thu, 10 May 2018 05:35:41 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, akpm@...ux-foundation.org,
        peterz@...radead.org, viro@...iv.linux.org.uk, mingo@...nel.org,
        paulmck@...ux.vnet.ibm.com, keescook@...omium.org, riel@...hat.com,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com,
        marcos.souza.org@...il.com, hoeun.ryu@...il.com,
        pasha.tatashin@...cle.com, gs051095@...il.com, dhowells@...hat.com,
        rppt@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH] cgroup: Don't mess with tasks in exec

Hello,

On Thu, May 10, 2018 at 02:15:32PM +0200, Oleg Nesterov wrote:
> > So avoid the problems by simply blocking cgroup migration over the
> > entirety of exec.
> 
> This patch, even if it was correct, will bring much more problems.
> 
> If nothing else exec() is very slow. If it races with migration which needs
> this sem for writing the new readers will be blocked. This means that clone(),
> exit(), or another exec() will block too.

Agreed.  I don't think it's a good idea to expand threadgroup coverage
larger than it already is.  I'd much prefer either working around the
copy_string case specifically or just ignoring it.

Thanks.

-- 
tejun