linux-kernel - Re: [PATCH V8 13/22] LoongArch: Add system call support

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Message-ID: <CAK8P3a38nUyAt8gGEYregqivdP7NsXS0RuU1NX4_EAVvwGQBWA@mail.gmail.com>
Date:   Mon, 21 Mar 2022 10:47:49 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH V8 13/22] LoongArch: Add system call support

On Mon, Mar 21, 2022 at 10:41 AM Huacai Chen <chenhuacai@...nel.org> wrote:
> On Mon, Mar 21, 2022 at 5:01 PM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > On Sat, Mar 19, 2022 at 3:38 PM Huacai Chen <chenhuacai@...nel.org> wrote:
> > >
> > > This patch adds system call support and related uaccess.h for LoongArch.
> > >
> > > Q: Why keep __ARCH_WANT_NEW_STAT definition while there is statx:
> > > A: Until the latest glibc release (2.34), statx is only used for 32-bit
> > >    platforms, or 64-bit platforms with 32-bit timestamp. I.e., Most 64-
> > >    bit platforms still use newstat now.
> > >
> > > Q: Why keep _ARCH_WANT_SYS_CLONE definition while there is clone3:
> > > A: The latest glibc release (2.34) has some basic support for clone3 but
> > >    it isn't complete. E.g., pthread_create() and spawni() have converted
> > >    to use clone3 but fork() will still use clone. Moreover, some seccomp
> > >    related applications can still not work perfectly with clone3.
> >
> > Please leave those out of the mainline kernel support though: Any users
> > of existing glibc binaries can keep using patched kernels for the moment,
> > and then later drop those pages when the proper glibc support gets
> > merged.
> The glibc commit d8ea0d0168b190bdf138a20358293c939509367f ("Add an
> internal wrapper for clone, clone2 and clone3") modified nearly
> everything in order to move to clone3(), except arch_fork() which used
> by fork(). And I cannot find any submitted patches to solve it. So I
> don't think this is just a forget, maybe there are other fundamental
> problems?

I don't think there are fundamental issues, they probably did not consider
it necessary because so far all architectures supported clone().

Adding Christian Brauner and H.J. Lu for clarificatoin.

> > > +#define __get_user(x, ptr) \
> > > +({                                                                     \
> > > +       int __gu_err = 0;                                               \
> > > +                                                                       \
> > > +       __chk_user_ptr(ptr);                                            \
> > > +       __get_user_common((x), sizeof(*(ptr)), ptr);                    \
> > > +       __gu_err;                                                       \
> > > +})
> >
> > It would be good to also provide a
> > __kernel_kernel_nofault()/__put_kernel_nofault()
> > implementation, as the default based on __get_user()/__put_user is not
> > ideal.
> They are provided in this file below.

Ok, I see them now, not sure what I did wrong when I looked earlier.

        Arnd