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

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Date:   Thu, 6 Jun 2019 13:05:22 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        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

On 06/06, David Laight wrote:
>
> 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?

See sigmask_to_save(), this is what the kernel records in uc.uc_sigmask
before the signal handler runs, after that current->saved_sigmask has no
meaning.

When signal handler returns it does sys_rt_sigreturn() which restores
the original mask saved in uc_sigmask.

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

See above.

Oleg.