linux-kernel - Re: [PATCH v4 7/8] pid: export pidfd_get

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Date:   Wed, 12 Feb 2020 16:25:31 -0800
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        linux-api@...r.kernel.org, oleksandr@...hat.com,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>
Subject: Re: [PATCH v4 7/8] pid: export pidfd_get_pid

On Wed, 2020-02-12 at 15:39 -0800, Minchan Kim wrote:
> process_madvise syscall needs pidfd_get_pid function to translate
> pidfd to pid so this patch exports the function.
> 
> Cc: Christian Brauner <christian@...uner.io>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

I think you might have misunderstood my earlier comments. This should be
patch 2 in your set. What is patch 8 should be folded into you existing
patch 2 and become patch 3 with the rest of your patches shifted by 1
since you are reordering them.

Otherwise the code itself appears to not have changed anything so it looks
fine to me.

Reviewed-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

> ---
>  include/linux/pid.h |  1 +
>  kernel/exit.c       | 17 -----------------
>  kernel/pid.c        | 17 +++++++++++++++++
>  3 files changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 998ae7d24450..023d9c3a8edc 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -75,6 +75,7 @@ extern const struct file_operations pidfd_fops;
>  struct file;
>  
>  extern struct pid *pidfd_pid(const struct file *file);
> +extern struct pid *pidfd_get_pid(unsigned int fd);
>  
>  static inline struct pid *get_pid(struct pid *pid)
>  {
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 0b81b26a872a..43375f9d8bbc 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1470,23 +1470,6 @@ static long do_wait(struct wait_opts *wo)
>  	return retval;
>  }
>  
> -static struct pid *pidfd_get_pid(unsigned int fd)
> -{
> -	struct fd f;
> -	struct pid *pid;
> -
> -	f = fdget(fd);
> -	if (!f.file)
> -		return ERR_PTR(-EBADF);
> -
> -	pid = pidfd_pid(f.file);
> -	if (!IS_ERR(pid))
> -		get_pid(pid);
> -
> -	fdput(f);
> -	return pid;
> -}
> -
>  static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
>  			  int options, struct rusage *ru)
>  {
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 0f4ecb57214c..360ba480a2a9 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -496,6 +496,23 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
>  	return idr_get_next(&ns->idr, &nr);
>  }
>  
> +struct pid *pidfd_get_pid(unsigned int fd)
> +{
> +	struct fd f;
> +	struct pid *pid;
> +
> +	f = fdget(fd);
> +	if (!f.file)
> +		return ERR_PTR(-EBADF);
> +
> +	pid = pidfd_pid(f.file);
> +	if (!IS_ERR(pid))
> +		get_pid(pid);
> +
> +	fdput(f);
> +	return pid;
> +}
> +
>  /**
>   * pidfd_create() - Create a new pid file descriptor.
>   *