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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 26 Nov 2019 20:04:08 -0800
Message-ID: <CAHk-=whrhuNg_53wc3pBVToH-AUwKDbC5P_cb7=8bYfn=BYCJA@mail.gmail.com>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix get_nr_restart_syscall()
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
        Jan Kratochvil <jan.kratochvil@redhat.com>,
        Pedro Alves <palves@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Tue, Nov 26, 2019 at 3:08 AM Oleg Nesterov <oleg@redhat.com> wrote:
>
> Alternatively we could add ->compat_restart into struct restart_block,
> logically this is the same thing.

That sounds like the better model to me. That's what the restart_block
is about: it's supposed to contain the restart information.

I'd much rather see the system call number added into the restart
block (or just the "compat bit" - but we have that X32 case too, so
why not put it all there). And then the get_nr_restart_syscall() hack
goes away and is just "set state from the restart block".

How painful would that be? I guess right now we always just set all
the restart_block info manually in all the restart cases, and that
could make it a bit painful to add this kind of architecture-specific
flag, but it _sounds_ conceptually like the right thing to do.

I definitely don't love the "magic sticky bit in thread status" field model.

             Linus