ext4: make ext4_es_lookup_extent() pass out the extent seq counter

When querying extents in the extent status tree, we should hold the
data_sem if we want to obtain the sequence number as a valid cookie
simultaneously. However, currently, ext4_map_blocks() calls
ext4_es_lookup_extent() without holding data_sem. Therefore, we should
acquire i_es_lock instead, which also ensures that the sequence cookie
and the extent remain consistent. Consequently, make
ext4_es_lookup_extent() to pass out the sequence number when necessary.

Signed-off-by: Zhang Yi <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/ext4/extents.c

···
 	while (block <= end) {
 		next = 0;
 		flags = 0;
-		if (!ext4_es_lookup_extent(inode, block, &next, &es))
+		if (!ext4_es_lookup_extent(inode, block, &next, &es, NULL))
 			break;
 		if (ext4_es_is_unwritten(&es))
 			flags |= FIEMAP_EXTENT_UNWRITTEN;

fs/ext4/extents_status.c

···
  * Return: 1 on found, 0 on not
  */
 int ext4_es_lookup_extent(struct inode *inode, ext4_lblk_t lblk,
-			  ext4_lblk_t *next_lblk,
-			  struct extent_status *es)
+			  ext4_lblk_t *next_lblk, struct extent_status *es,
+			  u64 *pseq)
 {
 	struct ext4_es_tree *tree;
 	struct ext4_es_stats *stats;
···
 			} else
 				*next_lblk = 0;
 		}
+		if (pseq)
+			*pseq = EXT4_I(inode)->i_es_seq;
 	} else {
 		percpu_counter_inc(&stats->es_stats_cache_misses);
 	}

fs/ext4/extents_status.h

···
 				      struct extent_status *es);
 extern int ext4_es_lookup_extent(struct inode *inode, ext4_lblk_t lblk,
 				 ext4_lblk_t *next_lblk,
-				 struct extent_status *es);
+				 struct extent_status *es, u64 *pseq);
 extern bool ext4_es_scan_range(struct inode *inode,
 			       int (*matching_fn)(struct extent_status *es),
 			       ext4_lblk_t lblk, ext4_lblk_t end);

fs/ext4/inode.c

···
 	 * extent status tree.
 	 */
 	if (flags & EXT4_GET_BLOCKS_PRE_IO &&
-	    ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es)) {
+	    ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es, NULL)) {
 		if (ext4_es_is_written(&es))
 			return retval;
 	}
···
 		ext4_check_map_extents_env(inode);
 
 	/* Lookup extent status tree firstly */
-	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es)) {
+	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es, NULL)) {
 		if (ext4_es_is_written(&es) || ext4_es_is_unwritten(&es)) {
 			map->m_pblk = ext4_es_pblock(&es) +
 					map->m_lblk - es.es_lblk;
···
 	ext4_check_map_extents_env(inode);
 
 	/* Lookup extent status tree firstly */
-	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es)) {
+	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es, NULL)) {
 		map->m_len = min_t(unsigned int, map->m_len,
 				   es.es_len - (map->m_lblk - es.es_lblk));
 
···
 	 * is held in write mode, before inserting a new da entry in
 	 * the extent status tree.
 	 */
-	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es)) {
+	if (ext4_es_lookup_extent(inode, map->m_lblk, NULL, &es, NULL)) {
 		map->m_len = min_t(unsigned int, map->m_len,
 				   es.es_len - (map->m_lblk - es.es_lblk));