Re: [PATCH 2/2] fs/locks: Remove fl_nspid and use fs-specific l_pid for remote locks

[Jeff Layton]

On Mon, 2017-06-19 at 09:24 -0400, Benjamin Coddington wrote:
> Since commit c69899a17ca4 "NFSv4: Update of VFS byte range lock must be
> atomic with the stateid update", NFSv4 has been inserting locks in rpciod
> worker context.  The result is that the file_lock's fl_nspid is the
> kworker's pid instead of the original userspace pid.
> 
> The fl_nspid is only used to represent the namespaced virtual pid number
> when displaying locks or returning from F_GETLK.  There's no reason to set
> it for every inserted lock, since we can usually just look it up from
> fl_pid.  So, instead of looking up and holding struct pid for every lock,
> let's just look up the virtual pid number from fl_pid when it is needed.
> That means we can remove fl_nspid entirely.
> 
> Also, if we're now 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.
> 
> Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> ---
>  fs/locks.c         | 70 +++++++++++++++++++++++++++++++++++-------------------
>  include/linux/fs.h |  2 +-
>  2 files changed, 46 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index d7daa6c8932f..206a46d28bbd 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -733,7 +733,6 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
>  static void
>  locks_insert_lock_ctx(struct file_lock *fl, struct list_head *before)
>  {
> -	fl->fl_nspid = get_pid(task_tgid(current));
>  	list_add_tail(&fl->fl_list, before);
>  	locks_insert_global_locks(fl);
>  }
> @@ -743,10 +742,6 @@ locks_unlink_lock_ctx(struct file_lock *fl)
>  {
>  	locks_delete_global_locks(fl);
>  	list_del_init(&fl->fl_list);
> -	if (fl->fl_nspid) {
> -		put_pid(fl->fl_nspid);
> -		fl->fl_nspid = NULL;
> -	}
>  	locks_wake_up_blocks(fl);
>  }
>  
> @@ -823,8 +818,6 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
>  	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
>  		if (posix_locks_conflict(fl, cfl)) {
>  			locks_copy_conflock(fl, cfl);
> -			if (cfl->fl_nspid)
> -				fl->fl_pid = pid_vnr(cfl->fl_nspid);
>  			goto out;
>  		}
>  	}
> @@ -2041,16 +2034,46 @@ 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;
>  }
>  EXPORT_SYMBOL_GPL(vfs_test_lock);
>  

I think this looks wrong for NFS.

There are really two cases we're concerned with here:

1) the lock is held by a task on the client itself, in which case we
probably want to report the pid as we would on a local fs.

...or...

2) the lock is held by another host entirely in which case the pid
doesn't have any meaning. We probably ought to return something like '-
1' as the pid (like we would for OFD locks).

The problem for NFS is that you're setting the flag unconditionally
there. It may very well be the case that we _want_ to translate the
fl_pid according to the local namespace (i.e. if the lock is held by a
task on the same host).

I think what you want to do here is have the fs ->lock operation set
that flag if the fl_pid should be used "as-is" instead of being
translated.

Most of the current lock operations can just set it early (to preserve
the existing behavior), but NFS could be set up to set that flag if the
lock request goes to the server.

> +/**
> + * locks_translate_pid - translate a pid number into a namespace
> + * @nr: The pid number in the init_pid_ns
> + * @ns: The namespace into which the pid should be translated
> + *
> + * Used to tranlate a fl_pid into a namespace virtual pid number
> + */
> +static pid_t locks_translate_pid(int init_nr, struct pid_namespace *ns)
> +{
> +	pid_t vnr;
> +	struct pid *pid;
> +
> +	rcu_read_lock();
> +	pid = find_pid_ns(init_nr, &init_pid_ns);
> +	vnr = pid_nr_ns(pid, ns);
> +	rcu_read_unlock();
> +	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
> @@ -2072,7 +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;
> @@ -2584,22 +2607,19 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>  {
>  	struct inode *inode = NULL;
>  	unsigned int fl_pid;
> +	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
>  
> -	if (fl->fl_nspid) {
> -		struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
> -
> -		/* Don't let fl_pid change based on who is reading the file */
> -		fl_pid = pid_nr_ns(fl->fl_nspid, 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
> -		 * called from __show_fd_info - skip lock entirely
> -		 */
> -		if (fl_pid == 0)
> -			return;
> -	} else
> +	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
> +	 * called from __show_fd_info - skip lock entirely
> +	 */
> +	if (fl_pid == 0)
> +		return;
>  
>  	if (fl->fl_file != NULL)
>  		inode = locks_inode(fl->fl_file);
> @@ -2674,7 +2694,7 @@ static int locks_show(struct seq_file *f, void *v)
>  
>  	fl = hlist_entry(v, struct file_lock, fl_link);
>  
> -	if (fl->fl_nspid && !pid_nr_ns(fl->fl_nspid, proc_pidns))
> +	if (locks_translate_pid(fl->fl_pid, proc_pidns) == 0)
>  		return 0;
>  
>  	lock_get_status(f, fl, iter->li_pos, "");
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index aa4affb38c39..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)
>  
> @@ -984,7 +985,6 @@ struct file_lock {
>  	unsigned char fl_type;
>  	unsigned int fl_pid;
>  	int fl_link_cpu;		/* what cpu's list is this on? */
> -	struct pid *fl_nspid;
>  	wait_queue_head_t fl_wait;
>  	struct file *fl_file;
>  	loff_t fl_start;

-- 
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>