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

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Message-ID: <20200622130155.GE6516@redhat.com>
Date:   Mon, 22 Jun 2020 15:01:55 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.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 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.

> > But this doesn't really matter. I mean, even if you race with another
> > thread doing exec/exit/whatever, current->sighand is stable. Unless, again,
> > current has already exited (called exit_notify()).

Oleg.