linux-kernel - Re: [PATCH v2 1/3] pidfd: extend pidfd_get

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Message-ID: <8c75620d-8920-4c19-8ebc-0f2b056d49fa@lucifer.local>
Date: Wed, 16 Oct 2024 07:05:44 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Christian Brauner <christian@...uner.io>, Shuah Khan <shuah@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, pedro.falcato@...il.com,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] pidfd: extend pidfd_get_pid() and de-duplicate
 pid lookup

On Tue, Oct 15, 2024 at 12:40:41PM -0700, Suren Baghdasaryan wrote:
[snip]
> > -struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
> > +struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid,
> > +                           bool allow_proc, unsigned int *flags,
> > +                           struct fd *fd)
> >  {
> > -       struct fd f;
> > +       struct file *file;
> >         struct pid *pid;
> > +       struct fd f = fdget(pidfd);
> >
> > -       f = fdget(fd);
> > -       if (!fd_file(f))
> > +       file = fd_file(f);
> > +       if (!file)
> >                 return ERR_PTR(-EBADF);
> >
> > -       pid = pidfd_pid(fd_file(f));
> > -       if (!IS_ERR(pid)) {
> > -               get_pid(pid);
> > -               *flags = fd_file(f)->f_flags;
> > +       pid = pidfd_pid(file);
> > +       /* If we allow opening a pidfd via /proc/<pid>, do so. */
> > +       if (IS_ERR(pid) && allow_proc)
> > +               pid = tgid_pidfd_to_pid(file);
> > +
> > +       if (IS_ERR(pid)) {
> > +               fdput(f);
> > +               return pid;
> >         }
> >
> > -       fdput(f);
> > +       if (pin_pid)
> > +               get_pid(pid);
> > +       else
> > +               WARN_ON_ONCE(!fd); /* Nothing to keep pid/pidfd around? */
> > +
> > +       if (flags)
> > +               *flags = file->f_flags;
> > +
> > +       /*
> > +        * If the user provides an fd output then it will handle decrementing
> > +        * its reference counter.
> > +        */
> > +       if (fd)
> > +               *fd = f;
> > +       else
> > +               /* Otherwise we release it. */
> > +               fdput(f);
> > +
> >         return pid;
> >  }
>
> There is an EXPORT_SYMBOL_GPL(pidfd_get_pid) right after this line. It
> should also be changed to EXPORT_SYMBOL_GPL(__pidfd_get_pid),
> otherwise __pidfd_get_pid() will not be exported. A module calling
> pidfd_get_pid() now inlined in the header file will try to call
> __pidfd_get_pid() and will have trouble resolving this symbol.

Hmm hang on not there isn't? I don't see that anywhere?

[snip]