btrfs: check io_ctl_prepare_pages return in __btrfs_write_out_cache

If io_ctl_prepare_pages fails, the pages in io_ctl.pages are not valid.
When we try to access them later, things will blow up in various ways.

Also fix the comment about the return value, which is an errno on error,
not -1, and update the cases where it was not.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Chris Mason <clm@fb.com>
(cherry picked from commit 2f2394735ce137d2862adaf9d0ce581136d5a157)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 253cb74b0e27eaa19a7caf3175f66f9576340aff..5a4f5d10ca35f7fccf540e8100c893aa3153763c 100644 (file)
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -1212,7 +1212,7 @@ out:
  *
  * This function writes out a free space cache struct to disk for quick recovery
  * on mount.  This will return 0 if it was successfull in writing the cache out,
- * and -1 if it was not.
+ * or an errno if it was not.
  */
 static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                                   struct btrfs_free_space_ctl *ctl,
@@ -1229,12 +1229,12 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
        int must_iput = 0;
 
        if (!i_size_read(inode))
-               return -1;
+               return -EIO;
 
        WARN_ON(io_ctl->pages);
        ret = io_ctl_init(io_ctl, inode, root, 1);
        if (ret)
-               return -1;
+               return ret;
 
        if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA)) {
                down_write(&block_group->data_rwsem);
@@ -1252,7 +1252,9 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
        }
 
        /* Lock all pages first so we can lock the extent safely. */
-       io_ctl_prepare_pages(io_ctl, inode, 0);
+       ret = io_ctl_prepare_pages(io_ctl, inode, 0);
+       if (ret)
+               goto out;
 
        lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
                         0, &cached_state);