btrfs: return real error from __filemap_get_folio() calls

We have a few places that always assume a -ENOMEM error happened in case a
call to __filemap_get_folio() returns an error, which is just too much of
an assumption and even if it would be the case at some point in time, it's
not future proof and there's nothing in the documentation that guarantees
that only ERR_PTR(-ENOMEM) can be returned with the flags we are passing
to it.

So use the exact error returned by __filemap_get_folio() instead.

Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: fdmanana

fs/btrfs/free-space-cache.c

@@ -457,7 +457,7 @@ static int io_ctl_prepare_pages(struct btrfs_io_ctl *io_ctl, bool uptodate)
 					    mask);
 		if (IS_ERR(folio)) {
 			io_ctl_drop_pages(io_ctl);
-			return -ENOMEM;
+			return PTR_ERR(folio);
 		}
 
 		ret = set_folio_extent_mapped(folio);

fs/btrfs/inode.c

@@ -4937,7 +4937,7 @@ int btrfs_truncate_block(struct btrfs_inode *inode, u64 offset, u64 start, u64 e
 			btrfs_delalloc_release_space(inode, data_reserved,
 						     block_start, blocksize, true);
 		btrfs_delalloc_release_extents(inode, blocksize);
-		ret = -ENOMEM;
+		ret = PTR_ERR(folio);
 		goto out;
 	}
 

fs/btrfs/reflink.c

@@ -87,7 +87,7 @@ static int copy_inline_to_page(struct btrfs_inode *inode,
 					FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
 					btrfs_alloc_write_mask(mapping));
 	if (IS_ERR(folio)) {
-		ret = -ENOMEM;
+		ret = PTR_ERR(folio);
 		goto out_unlock;
 	}