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Date:   Mon, 22 Jun 2020 15:04:01 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Dominique Martinet <asmadeus@codewreck.org>,
        Alexander Kapshuk <alexander.kapshuk@gmail.com>,
        linux-kernel@vger.kernel.org, ebiederm@xmission.com,
        akpm@linux-foundation.org, liuzhiqiang26@huawei.com,
        joel@joelfernandes.org, paulmck@linux.vnet.ibm.com,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] kernel/signal.c: Export symbol __lock_task_sighand
Message-ID: <20200622130401.obopyfdqpdnc5ydt@wittgenstein>
References: <20200621133704.77896-1-alexander.kapshuk@gmail.com>
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On Mon, Jun 22, 2020 at 03:01:55PM +0200, Oleg Nesterov wrote:
> On 06/22, Christian Brauner wrote:
> >
> > It is a supported case however unlikely. I just tried to answer
> > Dominique's specific question pointing out that even in that unlikely
> > case sighand_struct is stable.
> 
> I too tried to say this, but apparently just added more confusion ;)
> 
> > Just as an fyi, CLONE_SIGHAND with CLONE_VM but without CLONE_THREAD is
> > actually used quite a bit, e.g. in newlib, in stress-ng, and in criu.
> 
> OK,
> 
> > you'd want CLONE_VM which enforces
> > CLONE_SIGHAND so that would be another use-case afaict.
> 
> Cough no ;) CLONE_SIGHAND requires CLONE_VM, not vice versa.

Oh, you're right. I was thinking of ksys_unshare() here. :)

	/*
	 * If unsharing vm, must also unshare signal handlers.
	 */
	if (unshare_flags & CLONE_VM)
		unshare_flags |= CLONE_SIGHAND;

Thanks!
Christian