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Date:   Wed, 27 Nov 2019 18:02:35 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
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>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix
 get_nr_restart_syscall()
Message-ID: <20191127170234.GA26180@redhat.com>
References: <20191126110659.GA14042@redhat.com>
 <20191126110758.GA14051@redhat.com>
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On 11/26, Linus Torvalds wrote:
>
> 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 knew ;) OK, I won't argue, I'll send V2.

> 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).

apart from x86, who else can use it? after the quick grep I think nobody,
even arm64 and mips which have compat nr_restart's do not need it.

restart_block.arch_restart_block_infp makes more sense, but that would be
even more painful, I do not want to add asm/restart_block.h or
HAVE_ARCH_RESTART_INFO, or use CONFIG_IA32_EMULATION.

OK, lets add the new restart_block.nr_restart_syscall field, then we need

=09void set_restart_block_fn(restart, fn)
=09{
=09=09restart->nr_restart_syscall =3D arch_get_nr_restart_syscall()
=09=09restart->fn =3D fn;
=09}

but somehow I do not see a good place for

=09#ifndef arch_get_nr_restart_syscall()
=09#define arch_get_nr_restart_syscall()=090
=09#endif

Can you suggest a simple solution?

Hmm. Or may be HAVE_ARCH_RESTART is better after all? Say, just

=09--- a/include/linux/restart_block.h
=09+++ b/include/linux/restart_block.h
=09@@ -24,6 +24,9 @@ enum timespec_type {
=09  */
=09 struct restart_block {
=09=09long (*fn)(struct restart_block *);
=09+#ifdef=09CONFIG_HAVE_ARCH_RESTART_XXX
=09+=09int=09nr_restart_syscall;
=09+#endif
=09=09union {
=09=09=09/* For futex_wait and futex_wait_requeue_pi */
=09=09=09struct {
=09@@ -55,6 +58,15 @@ struct restart_block {
=09=09};
=09 };
=09=20
=09+static inline void set_restart_block_fn(restart, fn)
=09+{
=09+#ifdef=09CONFIG_HAVE_ARCH_RESTART_XXX
=09+=09extern int arch_get_nr_restart_syscall();
=09+=09restart->nr_restart_syscall =3D arch_get_nr_restart_syscall();
=09+#endif
=09+=09restart->fn =3D fn;
=09+}
=09+
=09 extern long do_no_restart_syscall(struct restart_block *parm);
=09=20
=09 #endif /* __LINUX_RESTART_BLOCK_H */

?

Oleg.