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Date:   Thu, 6 Jun 2019 13:05:22 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Linus Torvalds' <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Deepa Dinamani <deepa.kernel@gmail.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Davidlohr Bueso <dbueso@suse.de>, Jens Axboe <axboe@kernel.dk>,
        Davidlohr Bueso <dave@stgolabs.net>,
        "e@80x24.org" <e@80x24.org>, Jason Baron <jbaron@akamai.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        "linux-aio@kvack.org" <linux-aio@kvack.org>,
        "omar.kilani@gmail.com" <omar.kilani@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        stable <stable@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH -mm 0/1] signal: simplify
 set_user_sigmask/restore_user_sigmask
Message-ID: <20190606110522.GA4691@redhat.com>
References: <20190522032144.10995-1-deepa.kernel@gmail.com>
 <20190529161157.GA27659@redhat.com>
 <20190604134117.GA29963@redhat.com>
 <20190605155801.GA25165@redhat.com>
 <CAHk-=wjkNx8u4Mcm5dfSQKYQmLQAv1Z1yGLDZvty7BVSj4eqBA@mail.gmail.com>
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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.