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 0C8AAC433EF for ; Thu, 26 May 2022 14:25:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345442AbiEZOZj (ORCPT ); Thu, 26 May 2022 10:25:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57674 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345679AbiEZOZi (ORCPT ); Thu, 26 May 2022 10:25:38 -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 81890C5E51; Thu, 26 May 2022 07:25:36 -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 1A34A61B48; Thu, 26 May 2022 14:25:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 712A6C385A9; Thu, 26 May 2022 14:25:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653575135; bh=W7tj7X0phM9ahD0Hf4v7nQNVq951iFKg/FrRScsgPRI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=UFtiGo1CsYcwPCr5EjO22WjzXTWu8He/a5sTNyplgujEvmhS6TEno7+MAFntwxf+F itS4A/xIo7ZQnFuhzKFkuDq4rUIZkVzVBpMr7TH9OHanx/L7suCr5f0HF9wZkqpxnc VJm8Zs2klYzxdZX7+v5iI2/6MGghSp+kxNKeNHOwujidM0BI4LF+CflqQJOIVQDCSL lvKNBsa2FsulTUGaVN+EHgcuShXAtpyJ/CMseKxxDJuxdVYC2HaHgEGEfpFCytRRbQ 3WFy9+yYlO2OzaSULl8QS7vakz+CR8jeY7SKlgAXquh64N09d91nZgG0xp8tIXGwQz 6F7Q1B9LbElyg== Date: Thu, 26 May 2022 23:25:30 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt 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: <20220526232530.cb7d0aed0c60625ef093a735@kernel.org> In-Reply-To: <20220524192301.0c2ab08a@gandalf.local.home> References: <165189881197.175864.14757002789194211860.stgit@devnote2> <20220524192301.0c2ab08a@gandalf.local.home> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; 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: bpf@vger.kernel.org On Tue, 24 May 2022 19:23:01 -0400 Steven Rostedt wrote: > On Sat, 7 May 2022 13:46:52 +0900 > Masami Hiramatsu wrote: > > Is this expected to go through the BPF tree? > Yes, since rethook (fprobe) is currently used only from eBPF. Jiri, can you check this is good for your test case? Thank you, > -- 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; > -- Masami Hiramatsu (Google)