Previously ceph_readpage_to_fscache did not call if page was marked as cached
before calling fscache_write_page resulting in a BUG inside of fscache.
FS-Cache: Assertion failed
------------[ cut here ]------------
kernel BUG at fs/fscache/page.c:874!
invalid opcode: 0000 [#1] SMP
Call Trace:
 [<
ffffffffa02e6566>] __ceph_readpage_to_fscache+0x66/0x80 [ceph]
 [<
ffffffffa02caf84>] readpage_nounlock+0x124/0x210 [ceph]
 [<
ffffffffa02cb08d>] ceph_readpage+0x1d/0x40 [ceph]
 [<
ffffffff81126db6>] generic_file_aio_read+0x1f6/0x700
 [<
ffffffffa02c6fcc>] ceph_aio_read+0x5fc/0xab0 [ceph]
Signed-off-by: Milosz Tanski <milosz@adfin.com>
Signed-off-by: Sage Weil <sage@inktank.com>
        struct ceph_inode_info *ci = ceph_inode(inode);
        int ret;
 
+       if (!PageFsCache(page))
+               return;
+
        if (!cache_valid(ci))
                return;