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Date:   Thu, 10 May 2018 05:35:41 -0700
From:   Tejun Heo <tj@kernel.org>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, akpm@linux-foundation.org,
        peterz@infradead.org, viro@zeniv.linux.org.uk, mingo@kernel.org,
        paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com,
        tglx@linutronix.de, kirill.shutemov@linux.intel.com,
        marcos.souza.org@gmail.com, hoeun.ryu@gmail.com,
        pasha.tatashin@oracle.com, gs051095@gmail.com, dhowells@redhat.com,
        rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        Balbir Singh <balbir@linux.vnet.ibm.com>
Subject: Re: [RFC][PATCH] cgroup: Don't mess with tasks in exec
Message-ID: <20180510123541.GO2368884@devbig577.frc2.facebook.com>
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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