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Date: Thu, 6 Aug 2015 16:35:41 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, David Howells <dhowells@redhat.com>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness
Message-ID: <20150806143541.GA9414@redhat.com>
References: <20150728171500.GA2871@www.outflux.net> <20150728143504.5aa996ba5955522a19c2d5f1@linux-foundation.org> <20150728221111.GA23391@node.dhcp.inet.fi> <20150805172356.GA20490@redhat.com> <87wpx9sjhq.fsf@x220.int.ebiederm.org> <87614tr2jd.fsf@x220.int.ebiederm.org>
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On 08/05, Eric W. Biederman wrote:
>
> So I have to ask.

I hope you are asking someone else, not me ;) I never understood what
exactly we try to restrict and why.

> Is it possible to rework these checks such that we
> look at the sighand struct and signal sharing handling sharing instead
> of the count on the mm_struct?

Then why we can't simply check thread_group_empty() == T ? Why should we
worry about CLONE_SIGHAND at all?

Oleg.