linux-kernel - Re: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user

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Message-ID: <20190610162244.GB8127@redhat.com>
Date:   Mon, 10 Jun 2019 18:22:45 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        linux-kernel@...r.kernel.org, arnd@...db.de, dbueso@...e.de,
        axboe@...nel.dk, dave@...olabs.net, e@...24.org, jbaron@...mai.com,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        omar.kilani@...il.com, tglx@...utronix.de,
        Al Viro <viro@...IV.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Laight <David.Laight@...LAB.COM>,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask

On 06/07, Eric W. Biederman wrote:
>
> +static int set_sigmask(sigset_t *kmask)
> +{
> +	set_restore_sigmask();
> +	current->saved_sigmask = current->blocked;
> +	set_current_blocked(kmask);
> +
> +	return 0;
> +}

I was going to do the same change except my version returns void ;)

So ACK.

As for 2-5, sorry I can't read them today, will do tomorrow.

But at first glance... yes, we can remove TIF_RESTORE_SIGMASK.

As for "remove saved_sigmask" I have some concerns... At least this
means a user-visible change iiuc. Say, pselect unblocks a fatal signal.
Say, SIGINT without a handler. Suppose SIGINT comes after set_sigmask().

Before this change the process will be killed.

After this change it will be killed or not. It won't be killed if
do_select() finds an already ready fd without blocking, or it finds a
ready fd right after SIGINT interrupts poll_schedule_timeout().

And _to me_ the new behaviour makes more sense. But when it comes to
user-visible changes you can never know if it breaks something or not.

Oleg.