ext4: fix race when setting bitmap_uptodate flag

In ext4_read_{inode,block}_bitmap() we were setting bitmap_uptodate()
before submitting the buffer for read.  The is bad, since we check
bitmap_uptodate() without locking the buffer, and so if another
process is racing with us, it's possible that they will think the
bitmap is uptodate even though the read has not completed yet,
resulting in inodes and blocks potentially getting allocated more than
once if we get really unlucky.

Addresses-Google-Bug: 2828254

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 513004fc3d84..315f01be73e6 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1794,8 +1794,14 @@ extern struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb,
                                                     ext4_group_t block_group,
                                                     struct buffer_head ** bh);
 extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
-struct buffer_head *ext4_read_block_bitmap(struct super_block *sb,
-                                      ext4_group_t block_group);
+
+extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
+                                                ext4_group_t block_group);
+extern int ext4_wait_block_bitmap(struct super_block *sb,
+                                  ext4_group_t block_group,
+                                  struct buffer_head *bh);
+extern struct buffer_head *ext4_read_block_bitmap(struct super_block *sb,
+                                                  ext4_group_t block_group);
 extern void ext4_init_block_bitmap(struct super_block *sb,
                                    struct buffer_head *bh,
                                    ext4_group_t group,
@@ -1841,6 +1847,7 @@ extern void ext4_check_inodes_bitmap(struct super_block *);
 extern void ext4_mark_bitmap_end(int start_bit, int end_bit, char *bitmap);
 extern int ext4_init_inode_table(struct super_block *sb,
                                  ext4_group_t group, int barrier);
+extern void ext4_end_bitmap_read(struct buffer_head *bh, int uptodate);
 
 /* mballoc.c */
 extern long ext4_mb_stats;