linux-kernel - Re: [PATCH] kernel/signal.c: Export symbol __lock_task

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Date:   Mon, 22 Jun 2020 15:04:01 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Dominique Martinet <asmadeus@...ewreck.org>,
        Alexander Kapshuk <alexander.kapshuk@...il.com>,
        linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, liuzhiqiang26@...wei.com,
        joel@...lfernandes.org, paulmck@...ux.vnet.ibm.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] kernel/signal.c: Export symbol __lock_task_sighand

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