From: Christian Brauner <christian.brauner@xxxxxxxxxx> So far cachefiles only verified that the superblock wasn't read-only but didn't check whether the mount was. This made sense when we did not use a private mount because the read-only state could change at any point. Now that we have a private mount and mount properties can't change behind our back extend the read-only check to include the vfsmount. The __mnt_is_readonly() helper will check both the mount and the superblock. Note that before we checked root->d_sb and now we check mnt->mnt_sb but since we have a matching <vfsmount, dentry> pair here this is only syntactical change, not a semantic one. Here's how this works: mount -o ro --bind /var/cache/fscache/ /var/cache/fscache/ systemctl start cachefilesd Job for cachefilesd.service failed because the control process exited with error code. See "systemctl status cachefilesd.service" and "journalctl -xe" for details. dmesg | grep CacheFiles [ 2.922514] CacheFiles: Loaded [ 272.206907] CacheFiles: Failed to register: -30 errno 30 EROFS 30 Read-only file system Cc: David Howells <dhowells@xxxxxxxxxx> Cc: linux-cachefs@xxxxxxxxxx Cc: linux-fsdevel@xxxxxxxxxxxxxxx Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> --- fs/cachefiles/bind.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c index 7ef572d698f0..8cf283de4e14 100644 --- a/fs/cachefiles/bind.c +++ b/fs/cachefiles/bind.c @@ -141,8 +141,13 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache) !root->d_sb->s_op->sync_fs) goto error_unsupported; + /* + * Verify our mount and superblock aren't read-only. + * Note, while our private mount is guaranteed to not change anymore + * the superblock may still go read-only later. + */ ret = -EROFS; - if (sb_rdonly(root->d_sb)) + if (__mnt_is_readonly(cache->mnt)) goto error_unsupported; /* determine the security of the on-disk cache as this governs -- 2.27.0
