gfs2: Add flocks to glockfd debugfs file

Include flock glocks in the "glockfd" debugfs file.  Those are similar to the
iopen glocks; while an open file is holding an flock, it is holding the file's
flock glock.

We cannot take f_fl_mutex in gfs2_glockfd_seq_show_flock() or else dumping the
"glockfd" file would block on flock operations.  Instead, use the file->f_lock
spin lock to protect the f_fl_gh.gh_gl glock pointer.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/file.c

@@ -1444,6 +1444,22 @@ static int gfs2_lock(struct file *file, int cmd, struct file_lock *fl)
 		return dlm_posix_lock(ls->ls_dlm, ip->i_no_addr, file, cmd, fl);
 }
 
+static void __flock_holder_uninit(struct file *file, struct gfs2_holder *fl_gh)
+{
+	struct gfs2_glock *gl = fl_gh->gh_gl;
+
+	/*
+	 * Make sure gfs2_glock_put() won't sleep under the file->f_lock
+	 * spinlock.
+	 */
+
+	gfs2_glock_hold(gl);
+	spin_lock(&file->f_lock);
+	gfs2_holder_uninit(fl_gh);
+	spin_unlock(&file->f_lock);
+	gfs2_glock_put(gl);
+}
+
 static int do_flock(struct file *file, int cmd, struct file_lock *fl)
 {
 	struct gfs2_file *fp = file->private_data;
@@ -1475,7 +1491,9 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl)
 				       &gfs2_flock_glops, CREATE, &gl);
 		if (error)
 			goto out;
+		spin_lock(&file->f_lock);
 		gfs2_holder_init(gl, state, flags, fl_gh);
+		spin_unlock(&file->f_lock);
 		gfs2_glock_put(gl);
 	}
 	for (sleeptime = 1; sleeptime <= 4; sleeptime <<= 1) {
@@ -1486,7 +1504,7 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl)
 		msleep(sleeptime);
 	}
 	if (error) {
-		gfs2_holder_uninit(fl_gh);
+		__flock_holder_uninit(file, fl_gh);
 		if (error == GLR_TRYFAILED)
 			error = -EAGAIN;
 	} else {
@@ -1508,7 +1526,7 @@ static void do_unflock(struct file *file, struct file_lock *fl)
 	locks_lock_file_wait(file, fl);
 	if (gfs2_holder_initialized(fl_gh)) {
 		gfs2_glock_dq(fl_gh);
-		gfs2_holder_uninit(fl_gh);
+		__flock_holder_uninit(file, fl_gh);
 	}
 	mutex_unlock(&fp->f_fl_mutex);
 }

fs/gfs2/glock.c

@@ -2846,6 +2846,28 @@ static void gfs2_glockfd_seq_stop(struct seq_file *seq, void *iter_ptr)
 		put_task_struct(i->task);
 }
 
+static void gfs2_glockfd_seq_show_flock(struct seq_file *seq,
+					struct gfs2_glockfd_iter *i)
+{
+	struct gfs2_file *fp = i->file->private_data;
+	struct gfs2_holder *fl_gh = &fp->f_fl_gh;
+	struct lm_lockname gl_name = { .ln_type = LM_TYPE_RESERVED };
+
+	if (!READ_ONCE(fl_gh->gh_gl))
+		return;
+
+	spin_lock(&i->file->f_lock);
+	if (gfs2_holder_initialized(fl_gh))
+		gl_name = fl_gh->gh_gl->gl_name;
+	spin_unlock(&i->file->f_lock);
+
+	if (gl_name.ln_type != LM_TYPE_RESERVED) {
+		seq_printf(seq, "%d %u %u/%llx\n",
+			   i->tgid, i->fd, gl_name.ln_type,
+			   (unsigned long long)gl_name.ln_number);
+	}
+}
+
 static int gfs2_glockfd_seq_show(struct seq_file *seq, void *iter_ptr)
 {
 	struct gfs2_glockfd_iter *i = seq->private;
@@ -2859,6 +2881,7 @@ static int gfs2_glockfd_seq_show(struct seq_file *seq, void *iter_ptr)
 			   i->tgid, i->fd, gl->gl_name.ln_type,
 			   (unsigned long long)gl->gl_name.ln_number);
 	}
+	gfs2_glockfd_seq_show_flock(seq, i);
 	inode_unlock_shared(inode);
 	return 0;
 }