linux-kernel - RE: [PATCH v2] signal: Adjust error codes according to restore_user

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Date:   Tue, 28 May 2019 09:12:51 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Deepa Dinamani' <deepa.kernel@...il.com>,
        Oleg Nesterov <oleg@...hat.com>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Arnd Bergmann" <arnd@...db.de>, "dbueso@...e.de" <dbueso@...e.de>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>, Eric Wong <e@...24.org>,
        Jason Baron <jbaron@...mai.com>,
        "Linux FS-devel Mailing List" <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>,
        Omar Kilani <omar.kilani@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2] signal: Adjust error codes according to
 restore_user_sigmask()

From: Deepa Dinamani
> Sent: 24 May 2019 18:02
...
> Look at the code before 854a6ed56839a:
> 
>   /*
>         * If we changed the signal mask, we need to restore the original one.
>         * In case we've got a signal while waiting, we do not restore the
>         * signal mask yet, and we allow do_signal() to deliver the signal on
>         * the way back to userspace, before the signal mask is restored.
>         */
>        if (sigmask) {
>               ####### This err has not been changed since ep_poll()
>               ####### So if there is a signal before this point, but
> err = 0, then we goto else.
>                if (err == -EINTR) {
>                        memcpy(&current->saved_sigmask, &sigsaved,
>                               sizeof(sigsaved));
>                        set_restore_sigmask();
>                } else
>                      ############ This is a problem if there is signal
> pending that is sigmask should block.
>                      ########### This is the whole reason we have
> current->saved_sigmask?
>                        set_current_blocked(&sigsaved);
>        }

What happens if all that crap is just deleted (I presume from the
bottom of ep_wait()) ?

I'm guessing that on the way back to userspace signal handlers for
signals enabled in the process's current mask (the one specified
to epoll_pwait) get called.
Then the signal mask is loaded from current->saved_sigmask and
and enabled signal handlers are called again.
No special code there that depends on the syscall result, errno
of the syscall number.

That seems exactly correct!

	David

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