Btrfs: fix eb memory leak due to readpage failure

eb->io_pages is set in read_extent_buffer_pages().

In case of readpage failure, for pages that have been added to bio,
it calls bio_endio and later readpage_io_failed_hook() does the work.

When this eb's page (couldn't be the 1st page) fails to add itself to bio
due to failure in merge_bio(), it cannot decrease eb->io_pages via bio_endio,
 and ends up with a memory leak eventually.

This lets __do_readpage propagate errors to callers and adds the
 'atomic_dec(&eb->io_pages)'.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index ea12d0e..dae2f84 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2878,6 +2878,7 @@ __get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
  * into the tree that are removed when the IO is done (by the end_io
  * handlers)
  * XXX JDM: This needs looking at to ensure proper page locking
+ * return 0 on success, otherwise return error
  */
 static int __do_readpage(struct extent_io_tree *tree,
                         struct page *page,
@@ -2899,7 +2900,7 @@ static int __do_readpage(struct extent_io_tree *tree,
        sector_t sector;
        struct extent_map *em;
        struct block_device *bdev;
-       int ret;
+       int ret = 0;
        int nr = 0;
        size_t pg_offset = 0;
        size_t iosize;
@@ -3080,6 +3081,7 @@ static int __do_readpage(struct extent_io_tree *tree,
                } else {
                        SetPageError(page);
                        unlock_extent(tree, cur, cur + iosize - 1);
+                       goto out;
                }
                cur = cur + iosize;
                pg_offset += iosize;
@@ -3090,7 +3092,7 @@ out:
                        SetPageUptodate(page);
                unlock_page(page);
        }
-       return 0;
+       return ret;
 }
 
 static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
@@ -5230,14 +5232,31 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
        atomic_set(&eb->io_pages, num_reads);
        for (i = start_i; i < num_pages; i++) {
                page = eb->pages[i];
+
                if (!PageUptodate(page)) {
+                       if (ret) {
+                               atomic_dec(&eb->io_pages);
+                               unlock_page(page);
+                               continue;
+                       }
+
                        ClearPageError(page);
                        err = __extent_read_full_page(tree, page,
                                                      get_extent, &bio,
                                                      mirror_num, &bio_flags,
                                                      READ | REQ_META);
-                       if (err)
+                       if (err) {
                                ret = err;
+                               /*
+                                * We use &bio in above __extent_read_full_page,
+                                * so we ensure that if it returns error, the
+                                * current page fails to add itself to bio and
+                                * it's been unlocked.
+                                *
+                                * We must dec io_pages by ourselves.
+                                */
+                               atomic_dec(&eb->io_pages);
+                       }
                } else {
                        unlock_page(page);
                }