ext4: avoid ENOSPC when avoiding to reuse recently deleted inodes

When ext4 is running on a filesystem without a journal, it tries not to
reuse recently deleted inodes to provide better chances for filesystem
recovery in case of crash. However this logic forbids reuse of freed
inodes for up to 5 minutes and especially for filesystems with smaller
number of inodes can lead to ENOSPC errors returned when allocating new
inodes.

Fix the problem by allowing to reuse recently deleted inode if there's
no other inode free in the scanned range.
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200318121317.31941-1-jack@suse.czSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ialloc.c

@@ -712,21 +712,34 @@ static int recently_deleted(struct super_block *sb, ext4_group_t group, int ino)
 static int find_inode_bit(struct super_block *sb, ext4_group_t group,
 			  struct buffer_head *bitmap, unsigned long *ino)
 {
+	bool check_recently_deleted = EXT4_SB(sb)->s_journal == NULL;
+	unsigned long recently_deleted_ino = EXT4_INODES_PER_GROUP(sb);
+
 next:
 	*ino = ext4_find_next_zero_bit((unsigned long *)
 				       bitmap->b_data,
 				       EXT4_INODES_PER_GROUP(sb), *ino);
 	if (*ino >= EXT4_INODES_PER_GROUP(sb))
-		return 0;
+		goto not_found;
 
-	if ((EXT4_SB(sb)->s_journal == NULL) &&
-	    recently_deleted(sb, group, *ino)) {
+	if (check_recently_deleted && recently_deleted(sb, group, *ino)) {
+		recently_deleted_ino = *ino;
 		*ino = *ino + 1;
 		if (*ino < EXT4_INODES_PER_GROUP(sb))
 			goto next;
-		return 0;
+		goto not_found;
 	}
-
+	return 1;
+not_found:
+	if (recently_deleted_ino >= EXT4_INODES_PER_GROUP(sb))
+		return 0;
+	/*
+	 * Not reusing recently deleted inodes is mostly a preference. We don't
+	 * want to report ENOSPC or skew allocation patterns because of that.
+	 * So return even recently deleted inode if we could find better in the
+	 * given range.
+	 */
+	*ino = recently_deleted_ino;
 	return 1;
 }