From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9BDA6C433FE for ; Tue, 24 May 2022 23:23:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242603AbiEXXXH (ORCPT ); Tue, 24 May 2022 19:23:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52176 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235147AbiEXXXG (ORCPT ); Tue, 24 May 2022 19:23:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 40A135C879; Tue, 24 May 2022 16:23:05 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D265B617F1; Tue, 24 May 2022 23:23:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5EB5AC34100; Tue, 24 May 2022 23:23:03 +0000 (UTC) Date: Tue, 24 May 2022 19:23:01 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jiri Olsa , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH] rethook: Reject getting a rethook if RCU is not watching Message-ID: <20220524192301.0c2ab08a@gandalf.local.home> In-Reply-To: <165189881197.175864.14757002789194211860.stgit@devnote2> References: <165189881197.175864.14757002789194211860.stgit@devnote2> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, 7 May 2022 13:46:52 +0900 Masami Hiramatsu wrote: Is this expected to go through the BPF tree? -- Steve > Since the rethook_recycle() will involve the call_rcu() for reclaiming > the rethook_instance, the rethook must be set up at the RCU available > context (non idle). This rethook_recycle() in the rethook trampoline > handler is inevitable, thus the RCU available check must be done before > setting the rethook trampoline. > > This adds a rcu_is_watching() check in the rethook_try_get() so that > it will return NULL if it is called when !rcu_is_watching(). > > Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook") > Signed-off-by: Masami Hiramatsu > --- > kernel/trace/rethook.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c > index b56833700d23..c69d82273ce7 100644 > --- a/kernel/trace/rethook.c > +++ b/kernel/trace/rethook.c > @@ -154,6 +154,15 @@ struct rethook_node *rethook_try_get(struct rethook *rh) > if (unlikely(!handler)) > return NULL; > > + /* > + * This expects the caller will set up a rethook on a function entry. > + * When the function returns, the rethook will eventually be reclaimed > + * or released in the rethook_recycle() with call_rcu(). > + * This means the caller must be run in the RCU-availabe context. > + */ > + if (unlikely(!rcu_is_watching())) > + return NULL; > + > fn = freelist_try_get(&rh->pool); > if (!fn) > return NULL;