enforce ->sync_fs is only called for rw superblock
Make sure a superblock really is writeable by checking MS_RDONLY
under s_umount. sync_filesystems needed some re-arragement for
that, but all but one sync_filesystem caller had the correct locking
already so that we could add that check there. cachefiles grew
s_umount locking.
I've also added a WARN_ON to sync_filesystem to assert this for
future callers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index dafd484..431accd 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -354,7 +354,9 @@
/* make sure all pages pinned by operations on behalf of the netfs are
* written to disc */
cachefiles_begin_secure(cache, &saved_cred);
+ down_read(&cache->mnt->mnt_sb->s_umount);
ret = sync_filesystem(cache->mnt->mnt_sb);
+ up_read(&cache->mnt->mnt_sb->s_umount);
cachefiles_end_secure(cache, saved_cred);
if (ret == -EIO)