linux-kernel - Re: [PATCH 3/3] fs/locks: Use fs-specific l

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Message-ID: <1496835607.3703.1.camel@poochiereds.net>
Date:   Wed, 07 Jun 2017 07:40:07 -0400
From:   Jeff Layton <jlayton@...chiereds.net>
To:     Benjamin Coddington <bcodding@...hat.com>, bfields@...ldses.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] fs/locks: Use fs-specific l_pid for remote locks

On Tue, 2017-06-06 at 16:45 -0400, Benjamin Coddington wrote:
> Now that we're translating fl_pid for F_GETLK and /proc/locks, we need to
> handle the case where a remote filesystem directly sets fl_pid.  In that
> case, the fl_pid should not be translated into a local pid namespace.  If
> the filesystem implements the lock operation, set a flag to return the
> lock's fl_pid value directly, rather translate it.
> 

Actually, you're not translating anything for F_GETLK until we get to
this patch. Patch #2 in this series removes the fl_nspid field, but the
pid translation isn't fixed until here. That does mean a nominal
regression here in how fl_pid is reported between the two.

Would it be best to squash #2 and #3 together? Or maybe just go ahead
and universally translate the fl_pid field until you add the flag in
this patch?

Also to make sure I understand: task->tgid will always represent the
task's pid in the init_pid_ns, right?

Other than the minor bisectability concern, I think this looks good.
Nice work!

> Signed-off-by: Benjamin Coddington <bcodding@...hat.com>
> ---
>  fs/locks.c         | 22 ++++++++++++++++++----
>  include/linux/fs.h |  1 +
>  2 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 8d48e4c42ed3..206a46d28bbd 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2034,8 +2034,10 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
>   */
>  int vfs_test_lock(struct file *filp, struct file_lock *fl)
>  {
> -	if (filp->f_op->lock && is_remote_lock(filp))
> +	if (filp->f_op->lock && is_remote_lock(filp)) {
> +		fl->fl_flags |= FL_PID_PRIV;
>  		return filp->f_op->lock(filp, F_GETLK, fl);
> +	}
>  	posix_test_lock(filp, fl);
>  	return 0;
>  }
> @@ -2060,9 +2062,18 @@ static pid_t locks_translate_pid(int init_nr, struct pid_namespace *ns)
>  	return vnr;
>  }
>  
> +static pid_t flock_translate_pid(struct file_lock *fl)
> +{
> +	if (IS_OFDLCK(fl))
> +		return -1;
> +	if (fl->fl_flags & FL_PID_PRIV)
> +		return fl->fl_pid;
> +	return locks_translate_pid(fl->fl_pid,  task_active_pid_ns(current));
> +}
> +
>  static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
>  {
> -	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
> +	flock->l_pid = flock_translate_pid(fl);
>  #if BITS_PER_LONG == 32
>  	/*
>  	 * Make sure we can represent the posix lock via
> @@ -2084,7 +2095,7 @@ static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
>  #if BITS_PER_LONG == 32
>  static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
>  {
> -	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
> +	flock->l_pid = flock_translate_pid(fl);
>  	flock->l_start = fl->fl_start;
>  	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
>  		fl->fl_end - fl->fl_start + 1;
> @@ -2598,7 +2609,10 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>  	unsigned int fl_pid;
>  	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
>  
> -	fl_pid = locks_translate_pid(fl->fl_pid, proc_pidns);
> +	if (fl->fl_flags & FL_PID_PRIV)
> +		fl_pid = fl->fl_pid;
> +	else
> +		fl_pid = locks_translate_pid(fl->fl_pid, proc_pidns);
>  	/*
>  	 * If there isn't a fl_pid don't display who is waiting on
>  	 * the lock if we are called from locks_show, or if we are
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b013fac515f7..179496a9719d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -908,6 +908,7 @@ static inline struct file *get_file(struct file *f)
>  #define FL_UNLOCK_PENDING	512 /* Lease is being broken */
>  #define FL_OFDLCK	1024	/* lock is "owned" by struct file */
>  #define FL_LAYOUT	2048	/* outstanding pNFS layout */
> +#define FL_PID_PRIV	4096	/* F_GETLK should report fl_pid */
>  
>  #define FL_CLOSE_POSIX (FL_POSIX | FL_CLOSE)
>  

-- 
Jeff Layton <jlayton@...chiereds.net>