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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7A1D7C88E75 for ; Tue, 15 Sep 2026 13:13:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=4tD8a6exBiuiMZ+UoC5PJsvb3MP2QyoYGVvzltIQRI4=; b=rCb8jGrtZ6zXYbiRqk/6ttMuU1 h2L74zoisk2HFyqMfAR60gpsoN3dI6CGuxGadp6XEkjy0SUDMklEEphKaeYx4QBf3CBk6NsZEgzPx eQW9jUc2XRM4PCVv7Ov/sF7KJUInQoPURFoggJsh9CHfmDdRZvlUQjxWI/O0BwQwka/K9crCiH0Qa Fs6NKVaZM4MJSr2+XrrAD+/kLfq20gspsJFRYXERUukTiIUy2q9uNQEUtZ/y/4eGcSM7UEHfVYCUK xwdVFPDDWe3mPqSJPpLsNK9lC7G3p0yVFwQy8D0KQMGv8Yrxmu3Sy/pYjXlqDsxzwbtlN9tLpvySJ 0F4Zts1Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6SyV-00000006fmO-3xwK; Tue, 15 Sep 2026 13:13:27 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6SyU-00000006fm2-2mO5 for linux-arm-kernel@lists.infradead.org; Tue, 15 Sep 2026 13:13:26 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 17A9D43572; Tue, 15 Sep 2026 13:13:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54BE11F0089A; Tue, 15 Sep 2026 13:13:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789478006; bh=4tD8a6exBiuiMZ+UoC5PJsvb3MP2QyoYGVvzltIQRI4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Knl5Rk7L79lys25DYi750mDQwSC6ffBx2Yd/MV/TjslA4t980FAtpJisR/xidrHPa 6T6sVPQ0O8X3eLpZ4aarQrxyNuteXmYp3jFjVCIelAbEeqFmpJ0aG+1p7qWMugMF2G WnMT63DNSgDMnE4a4bsyEHD0XV1F9aDohAhutgwte6vXVNl4dHGI/2KBmBhezBvpJx 3GnTUXWxqs+EZxgeUrMfbLe6QI7ea2Bw2jnSpd87qTMVX6qIeb9u4IYVif7vUzusPZ 1kTqjhRNVP4VMysH92GYpVpSFfauL7AkXQtXSNc7pu9ap+gUdQdJdoxv0udHzAQgmY SX9YeTJ0eXJvg== Date: Tue, 15 Sep 2026 15:13:23 +0200 From: Frederic Weisbecker To: Josef Bacik Cc: "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , x86@kernel.org, Catalin Marinas , Will Deacon , Puranjay Mohan , Xu Kuohai , Andy Lutomirski , Josh Triplett , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juergen Gross , Luis Chamberlain , Ihor Solodrai , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH RFC v2 03/15] rcu-tasks: Hold trampoline nesting across irq-exit preemption in trampoline text Message-ID: References: <20260911-b4-rcu-tasks-preempt-qs-v2-0-eaaa61ed2da4@toxicpanda.com> <20260911-b4-rcu-tasks-preempt-qs-v2-3-eaaa61ed2da4@toxicpanda.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260911-b4-rcu-tasks-preempt-qs-v2-3-eaaa61ed2da4@toxicpanda.com> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Le Fri, Sep 11, 2026 at 02:08:41PM +0000, Josef Bacik a écrit : > A trampoline's own rcu_tramp_nesting increment and decrement live inside > the trampoline, so there is a window of a few instructions on entry and > exit where the count is zero while the CPU is executing trampoline text > (or text on the way into one, such as a static ftrace stub holding a > direct-call target). In that window the task has not called out, so it > can only be preempted from an interrupt, and the interrupted instruction > pointer identifies where it is. I haven't read the whole patchset yet but what happens if the count is zero on trampoline exit but the trampoline isn't finished yet and RCU tasks does a fully quiescent scan of all tasks during that short window? Isn't that ending with a too short grace period? Thanks. -- Frederic Weisbecker SUSE Labs