linux-kernel - RE: [PATCH -mm 0/1] signal: simplify set_user_sigmask/restore_user

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Date:   Thu, 6 Jun 2019 09:05:21 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Davidlohr Bueso" <dbueso@...e.de>, Jens Axboe <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>,
        "e@...24.org" <e@...24.org>, Jason Baron <jbaron@...mai.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "omar.kilani@...il.com" <omar.kilani@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        stable <stable@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: RE: [PATCH -mm 0/1] signal: simplify
 set_user_sigmask/restore_user_sigmask

From: Linus Torvalds
> Sent: 05 June 2019 18:25
> On Wed, Jun 5, 2019 at 8:58 AM Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > To simplify the review, please see the code with this patch applied.
> > I am using epoll_pwait() as an example because it looks very simple.
> 
> I like it.
> 
> However.
> 
> I think I'd like it even more if we just said "we don't need
> restore_saved_sigmask AT ALL".
> 
> Which would be fairly easy to do with something like the attached...

That would always call the signal handlers even when EINTR wasn't
being returned (which I think ought to happen ...).
The real purpose of restore_saved_sigmask() is to stop signal
handlers that are enabled by the temporary mask being called.

If a signal handler is called, I presume that the trampoline
calls back into the kernel to get further handlers called
and to finally restore the original signal mask?

What happens if a signal handler calls something that
would normally write to current->saved_sigmask?

	David

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