erofs: fix erofs_get_meta_page locking due to a cleanup

After doing more drop_caches stress test on
our products, I found the mistake introduced by
a very recent cleanup [1].

The current rule is that "erofs_get_meta_page"
should be returned with page locked (although
it's mostly unnecessary for read-only fs after
pages are PG_uptodate), but a fix should be
done for this.

[1] https://lore.kernel.org/r/20190904020912.63925-26-gaoxiang25@huawei.com
Fixes: 618f40ea026b ("erofs: use read_cache_page_gfp for erofs_get_meta_page")
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20190921184355.149928-1-gaoxiang25@huawei.com
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 8a9fcbd0e8ac197fbe22d04c23fc66bb9feff7b8..fc3a8d8064f84f8ee1ce24787c2632ca17c09650 100644 (file)
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -34,11 +34,15 @@ static void erofs_readendio(struct bio *bio)
 
 struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr)
 {
-       struct inode *const bd_inode = sb->s_bdev->bd_inode;
-       struct address_space *const mapping = bd_inode->i_mapping;
+       struct address_space *const mapping = sb->s_bdev->bd_inode->i_mapping;
+       struct page *page;
 
-       return read_cache_page_gfp(mapping, blkaddr,
+       page = read_cache_page_gfp(mapping, blkaddr,
                                   mapping_gfp_constraint(mapping, ~__GFP_FS));
+       /* should already be PageUptodate */
+       if (!IS_ERR(page))
+               lock_page(page);
+       return page;
 }
 
 static int erofs_map_blocks_flatmode(struct inode *inode,