Received: by 2002:a25:1506:0:0:0:0:0 with SMTP id 6csp270774ybv; Wed, 5 Feb 2020 05:21:23 -0800 (PST) X-Google-Smtp-Source: APXvYqyDvpUnhEAsu/0S6epNUSXRHNMrFS7R8MfFU7mex7wCj+mWNqtEKTTDAcxHLdlWmNyOtiy/ X-Received: by 2002:a05:6830:140b:: with SMTP id v11mr25797472otp.340.1580908883822; Wed, 05 Feb 2020 05:21:23 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1580908883; cv=none; d=google.com; s=arc-20160816; b=iY+elD2nyN3bRjPJxRyyX2+nicKqBZGuIesuyyVVLb4IBWVkTTY/xOC4QbYfG/wpDh ZI0F5pjpS0B34UPtLTEf0dq8kBTZt13a9786HTNuPG/gkYTRMj2t0c2gPGvDeku5+ICS FRrZIEdC5NUEnkOTxOQqGpcU5yKNToQeXqh/0VH6yQPyMnzioNPdIAIK5TFTeTz6JKFm OMrOFzzFeWqKapNes6Y27yu5VgbN1WflCORX0BCQDWArhhrwGHSxrolqPBvpI1/XOzWH 1FmKuomGZDYn2UDgcDfR3AqbIJldfYMzA1aEIeEmeZ1Au5Si3uEwHa3xAtKnF+xkHLZN K5DQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding:mime-version :references:in-reply-to:message-id:subject:cc:to:from:date; bh=Sii+tqOBJRzooh7WgIqHGQ4Y5B1dO8RTk7dtboMEl1s=; b=LMPWYNAVdeoSzxDGxypOExk+u83vnZJPcVdoE3jWS0Bp5Lf3frNerahoMlWBqNp4UJ gAvmgb3+5UdmZrlvwj7+d1fiopiqkdMqq2teZL9nz0XZphmrdHy9ZzRWCdpHyFpf/c6D diVIdvEo0/muK1Aw5L9cKTdSsTiMlleYPBIPAEPlDgLBV+LDW2RJWsuQjoGVWICS2A/g edNfgRfeXQbA7GHCZrcfHHT/ROhxHP9wCM/1OG/0khP7xcZyus/PvjnwGzDQiCR9rTf8 EbdWX531leOIu3NA0VlM7OGjjP9xFIZTrsrHjRXKSQkJthZ7CyM39166RLoJIIS+5yIZ xVKA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id 22si5897806oin.34.2020.02.05.05.21.11; Wed, 05 Feb 2020 05:21:23 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727458AbgBENT2 (ORCPT + 99 others); Wed, 5 Feb 2020 08:19:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:36672 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726822AbgBENT2 (ORCPT ); Wed, 5 Feb 2020 08:19:28 -0500 Received: from oasis.local.home (unknown [212.187.182.165]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D349A217BA; Wed, 5 Feb 2020 13:19:25 +0000 (UTC) Date: Wed, 5 Feb 2020 08:19:21 -0500 From: Steven Rostedt To: "Paul E. McKenney" Cc: Joel Fernandes , Amol Grover , Ingo Molnar , linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, Madhuparna Bhowmik Subject: Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu Message-ID: <20200205081921.34b19d9a@oasis.local.home> In-Reply-To: <20200205081409.4550aa67@oasis.local.home> References: <20200201072703.17330-1-frextrite@gmail.com> <20200203163301.GB85781@google.com> <20200204200116.479f0c60@oasis.local.home> <20200205131110.GT2935@paulmck-ThinkPad-P72> <20200205081409.4550aa67@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Feb 2020 08:14:09 -0500 Steven Rostedt wrote: > On Wed, 5 Feb 2020 05:11:10 -0800 > "Paul E. McKenney" wrote: > > > I strongly recommend a comment stating why disabling preemption prevents > > ftrace_graph_hash from going away. I see the synchronize_rcu() after > > the rcu_assign_pointer() in ftrace_graph_release(), but I don't see > > anything that waits on CPUs that RCU is not watching. > > > > Of course, event tracing -makes- RCU watch when needed, but if that > > was set up, then lockdep would not have complained. > > > > So what am I missing? > > Keep looking in your INBOX and look at the patch I asked you to ack or > complain about ;-) Actually, looking at the code myself, it appears to be missing the ftrace_sync. Thus, this is a bug, and requires the ftrace sync, as synchronize_rcu() is not strong enough here. Patch in process! -- Steve