[PATCH 1/4] cachefiles: Fix corruption of the return value in cachefiles_read_or_alloc_pages()

[David Howells]

The patch which changed cachefiles from calling ->bmap() to using the
bmap() wrapper overwrote the running return value with the result of
calling bmap().  This causes an assertion failure elsewhere in the code.

Fix this by using ret2 rather than ret to hold the return value.

The oops looks like:

        kernel BUG at fs/nfs/fscache.c:468!
        ...
        RIP: 0010:__nfs_readpages_from_fscache+0x18b/0x190 [nfs]
        ...
        Call Trace:
         nfs_readpages+0xbf/0x1c0 [nfs]
         ? __alloc_pages_nodemask+0x16c/0x320
         read_pages+0x67/0x1a0
         __do_page_cache_readahead+0x1cf/0x1f0
         ondemand_readahead+0x172/0x2b0
         page_cache_async_readahead+0xaa/0xe0
         generic_file_buffered_read+0x852/0xd50
         ? mem_cgroup_commit_charge+0x6e/0x140
         ? nfs4_have_delegation+0x19/0x30 [nfsv4]
         generic_file_read_iter+0x100/0x140
         ? nfs_revalidate_mapping+0x176/0x2b0 [nfs]
         nfs_file_read+0x6d/0xc0 [nfs]
         new_sync_read+0x11a/0x1c0
         __vfs_read+0x29/0x40
         vfs_read+0x8e/0x140
         ksys_read+0x61/0xd0
         __x64_sys_read+0x1a/0x20
         do_syscall_64+0x60/0x1e0
         entry_SYSCALL_64_after_hwframe+0x44/0xa9
        RIP: 0033:0x7f5d148267e0

Fixes: 10d83e11a582 ("cachefiles: drop direct usage of ->bmap method.")
Reported-by: David Wysochanski <dwyso...@redhat.com>
Signed-off-by: David Howells <dhowe...@redhat.com>
Tested-by: David Wysochanski <dwyso...@redhat.com>
cc: Carlos Maiolino <cmaiol...@redhat.com>
---

 fs/cachefiles/rdwr.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 1dc97f2d6201..d3d78176b23c 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -398,7 +398,7 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval 
*op,
        struct inode *inode;
        sector_t block;
        unsigned shift;
-       int ret;
+       int ret, ret2;
 
        object = container_of(op->op.object,
                              struct cachefiles_object, fscache);
@@ -430,8 +430,8 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval 
*op,
        block = page->index;
        block <<= shift;
 
-       ret = bmap(inode, &block);
-       ASSERT(ret < 0);
+       ret2 = bmap(inode, &block);
+       ASSERT(ret2 == 0);
 
        _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 == 0);
 
                _debug("%llx -> %llx",
                       (unsigned long long) (page->index << shift),