On Tue, 19 Sep 2023 18:41:09 +0900 Masami Hiramatsu (Google) <mhira...@kernel.org> wrote:
> > > > ti = get_tracefs(inode); > > > > if (!(ti->flags & TRACEFS_EVENT_INODE)) > > > > @@ -375,10 +485,18 @@ static int eventfs_release(struct inode *inode, > > > > struct file *file) > > > > > > > > ei = ti->private; > > > > idx = srcu_read_lock(&eventfs_srcu); > > > > - list_for_each_entry_srcu(ef, &ei->e_top_files, list, > > > > + list_for_each_entry_srcu(ei_child, &ei->children, list, > > > > srcu_read_lock_held(&eventfs_srcu)) { > > > > mutex_lock(&eventfs_mutex); > > > > - dentry = ef->dentry; > > > > + dentry = ei_child->dentry; > > > > + mutex_unlock(&eventfs_mutex); > > > > > > If someone add a directory via eventfs_create_dir() in parallel, is this > > > local mutex_lock able to protect from that? (usually it may not happen.) > > > > That would require an event being added and created at the same time. Not > > sure that is possible. > > > > We could try it? > > Not sure, but both eventfs_release() and eventfs_create_dir() will be > called from dynamic events, right? But the dynamic events will protect > the create/delete operation with a mutex, so it should not happen if > I understand correctly. > But if the eventfs requires such external exclusion for the operation, > it should be commented. Hmm, actually looking at this, it's worse than what you stated. This is called when a directory is closed. So if you had: open(dir); // look at all the content of this dir to create dentries // another task creates a new entry and looks at it too. close(dir); Now we iterate over all the dentries of the dir and dput it. I think this will cause the ref counts to get out of sync. I'll have to try to create this scenario and see what happens. > > > > > > > > > > + if (dentry) > > > > + dput(dentry); > > > > + } > > > > + > > > > + for (i = 0; i < ei->nr_entries; i++) { > > > > + mutex_lock(&eventfs_mutex); > > > > + dentry = ei->d_children[i]; > > > > mutex_unlock(&eventfs_mutex); > > > > > > Ditto. Maybe I'm misunderstanding how eventfs_mutex is used. > > > > I'll have to go back and look at this part on why I had this. I think it > > was to make sure ei->d_children existed. But it may also need a test too. I > > don't remember. :-/ I believe this is to keep this and create_file_dentry() in sync. But I need to look deeper. I'm still very new with understanding how all this file system code works :-p -- Steve