gfs2: Use gfs2 wrapper to sync inode before calling generic_file_splice_read()

gfs2_file_splice_read() f_op grabs and releases the cluster-wide
inode glock to sync the inode size to the latest.

Without this, generic_file_splice_read() uses an older i_size value
and can return EOF for valid offsets in the inode.
Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/file.c

@@ -950,6 +950,30 @@ static long gfs2_fallocate(struct file *file, int mode, loff_t offset, loff_t le
 	return ret;
 }
 
+static ssize_t gfs2_file_splice_read(struct file *in, loff_t *ppos,
+				     struct pipe_inode_info *pipe, size_t len,
+				     unsigned int flags)
+{
+	struct inode *inode = in->f_mapping->host;
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_holder gh;
+	int ret;
+
+	mutex_lock(&inode->i_mutex);
+
+	ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
+	if (ret) {
+		mutex_unlock(&inode->i_mutex);
+		return ret;
+	}
+
+	gfs2_glock_dq_uninit(&gh);
+	mutex_unlock(&inode->i_mutex);
+
+	return generic_file_splice_read(in, ppos, pipe, len, flags);
+}
+
+
 static ssize_t gfs2_file_splice_write(struct pipe_inode_info *pipe,
 				      struct file *out, loff_t *ppos,
 				      size_t len, unsigned int flags)
@@ -1112,7 +1136,7 @@ const struct file_operations gfs2_file_fops = {
 	.fsync		= gfs2_fsync,
 	.lock		= gfs2_lock,
 	.flock		= gfs2_flock,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= gfs2_file_splice_read,
 	.splice_write	= gfs2_file_splice_write,
 	.setlease	= simple_nosetlease,
 	.fallocate	= gfs2_fallocate,
@@ -1140,7 +1164,7 @@ const struct file_operations gfs2_file_fops_nolock = {
 	.open		= gfs2_open,
 	.release	= gfs2_release,
 	.fsync		= gfs2_fsync,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= gfs2_file_splice_read,
 	.splice_write	= gfs2_file_splice_write,
 	.setlease	= generic_setlease,
 	.fallocate	= gfs2_fallocate,