The commit, cachefiles: drop direct usage of ->bmap method., included in v5.5 has a bug. The return value before list_for_each_entry_safe, that is ret = space ? -ENODATA : -ENOBUFS, overwritten by the return value of bmap. This bug exists in Linux 5.6.2 at least.
The following is a patch to fix this bug. This patch also includes https://lkml.org/lkml/2020/3/20/399.
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -431,7 +431,7 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
block <<= shift;
ret = bmap(inode, &block);
- ASSERT(ret < 0);
+ ASSERT(!ret);
_debug("%llx -> %llx",
(unsigned long long) (page->index << shift),
@@ -739,8 +739,8 @@ int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
block = page->index;
block <<= shift;
- ret = bmap(inode, &block);
- ASSERT(!ret);
+ ret2 = bmap(inode, &block);
+ ASSERT(!ret2);
_debug("%llx -> %llx",
(unsigned long long) (page->index << shift),
Update (2020/5/24)
This bug has been fixed in Linux 5.6.14 while fixed in v5.7-rc6 as for the master branch.