fs/locks: Remove fl_nspid and use fs-specific l_pid for remote locks

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.

The translaton and presentation of fl_pid should handle the following four
cases:

1 - F_GETLK on a remote file with a remote lock:
    In this case, the filesystem should determine the l_pid to return here.
    Filesystems should indicate that the fl_pid represents a non-local pid
    value that should not be translated by returning an fl_pid <= 0.

2 - F_GETLK on a local file with a remote lock:
    This should be the l_pid of the lock manager process, and translated.

3 - F_GETLK on a remote file with a local lock, and
4 - F_GETLK on a local file with a local lock:
    These should be the translated l_pid of the local locking process.

Fuse was already doing the correct thing by translating the pid into the
caller's namespace.  With this change we must update fuse to translate
to init's pid namespace, so that the locks API can then translate from
init's pid namespace into the pid namespace of the caller.

With this change, the locks API will expect that if a filesystem returns
a remote pid as opposed to a local pid for F_GETLK, that remote pid will
be <= 0.  This signifies that the pid is remote, and the locks API will
forego translating that pid into the pid namespace of the local calling
process.

Finally, we convert remote filesystems to present remote pids using
negative numbers. Have lustre, 9p, ceph, cifs, and dlm negate the remote
pid returned for F_GETLK lock requests.

Since local pids will never be larger than PID_MAX_LIMIT (which is
currently defined as <= 4 million), but pid_t is an unsigned int, we
should have plenty of room to represent remote pids with negative
numbers if we assume that remote pid numbers are similarly limited.

If this is not the case, then we run the risk of having a remote pid
returned for which there is also a corresponding local pid.  This is a
problem we have now, but this patch should reduce the chances of that
occurring, while also returning those remote pid numbers, for whatever
that may be worth.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>

1 files changed, 37 insertions, 25 deletions

diff --git a/fs/locks.c b/fs/locks.c
index d7daa6c8932f..6d0949880ebd 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -137,6 +137,7 @@
 #define IS_FLOCK(fl)	(fl->fl_flags & FL_FLOCK)
 #define IS_LEASE(fl)	(fl->fl_flags & (FL_LEASE|FL_DELEG|FL_LAYOUT))
 #define IS_OFDLCK(fl)	(fl->fl_flags & FL_OFDLCK)
+#define IS_REMOTELCK(fl)	(fl->fl_pid <= 0)
 
 static inline bool is_remote_lock(struct file *filp)
 {
@@ -733,7 +734,6 @@ 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 +743,6 @@ 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 +819,6 @@ 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;
 		}
 	}
@@ -2048,9 +2042,33 @@ int vfs_test_lock(struct file *filp, struct file_lock *fl)
 }
 EXPORT_SYMBOL_GPL(vfs_test_lock);
 
+/**
+ * locks_translate_pid - translate a file_lock's fl_pid number into a namespace
+ * @fl: The file_lock who's fl_pid should be translated
+ * @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(struct file_lock *fl, struct pid_namespace *ns)
+{
+	pid_t vnr;
+	struct pid *pid;
+
+	if (IS_OFDLCK(fl))
+		return -1;
+	if (IS_REMOTELCK(fl))
+		return fl->fl_pid;
+
+	rcu_read_lock();
+	pid = find_pid_ns(fl->fl_pid, &init_pid_ns);
+	vnr = pid_nr_ns(pid, ns);
+	rcu_read_unlock();
+	return vnr;
+}
+
 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 = locks_translate_pid(fl, task_active_pid_ns(current));
 #if BITS_PER_LONG == 32
 	/*
 	 * Make sure we can represent the posix lock via
@@ -2072,7 +2090,7 @@ 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 = locks_translate_pid(fl, task_active_pid_ns(current));
 	flock->l_start = fl->fl_start;
 	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
 		fl->fl_end - fl->fl_start + 1;
@@ -2584,22 +2602,16 @@ 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
-		fl_pid = fl->fl_pid;
+	fl_pid = locks_translate_pid(fl, 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 +2686,7 @@ 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, proc_pidns) == 0)
 		return 0;
 
 	lock_get_status(f, fl, iter->li_pos, "");