From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C6E2F1EEE4 for ; Wed, 4 Sep 2024 13:48:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725457685; cv=none; b=OuD1WI5awUHFUwEtdK9twPcDc+jNKgi+ba7aRNl8KEtOrDcMQbFJkRXbzYCa5relFKobmqxqpxD3nj/uQjmOlFlFcLeaLRHPcl1S0NpDbXCiDks0sv9PKWrsV8qWUIwXABD9amixvG+a0a1ssyWxY5sPGMbDCgkjNY98+b7kLZ4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725457685; c=relaxed/simple; bh=JJL+01nioC8/SeoOsSQSCyYRdVM5b2GJMKeQql93LUQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MEV6YaMCYq4QKetCxGiiXEA7jpwKyFOQWZNbgfPuPjPwQYKlNVGS2/q7x7TFJ3Y/PeD/d+YEEOtWwO55qF7bRoZ0TQCwc9N2EbczPUgpQCOZBHyIxJbiMOoKumA3yfMVtViiL6cIenF3OfvLF53jT130tLwY5sqOiO1kd1ByJew= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=USj0ndVE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="USj0ndVE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F216C4CEC2; Wed, 4 Sep 2024 13:48:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725457685; bh=JJL+01nioC8/SeoOsSQSCyYRdVM5b2GJMKeQql93LUQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=USj0ndVEArtTb8o0Ojs039jHBerVNoJ54eSz8tGnurmLj9o7TonB6QRyftpn+pKS6 mSWT65h9ict1nnXdlgr/nQIrZhsj3vAvVck5ltG31OukLnKqotNDnRu1HF0WdIzYnB AbdlypnSjEY5ilo0Prw6cMu3Kp37qIQnhbTO74wxc03U7cjCOi+3NlLYDgcIuuYY9V /9Sw95uPE7uBdxYEd1TapkAm9dNYJF/UXXDust35BmtjZFEqFZVLlst5QuELnWVSeV 5mMg0kTEeXIqFFK2WimMThqKzESOoMQfz1vRu6LkTeB2k507U+LNefDTqrfSgaMdtC qgcu1nHyBMkCg== Date: Wed, 4 Sep 2024 15:48:02 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Z qiang , rcu@vger.kernel.org Subject: Re: One-off rcu_nocb_rdp_deoffload bug Message-ID: References: <2747e596-5359-4f32-b3e0-0b2368d37017@paulmck-laptop> <236a1f66-f128-44e4-9272-7ae4dbad7485@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <236a1f66-f128-44e4-9272-7ae4dbad7485@paulmck-laptop> Le Wed, Sep 04, 2024 at 05:59:46AM -0700, Paul E. McKenney a écrit : > On Tue, Aug 20, 2024 at 10:46:43AM -0700, Paul E. McKenney wrote: > > On Tue, Aug 20, 2024 at 04:43:39PM +0200, Frederic Weisbecker wrote: > > > Sorry for the html mail, I only have my phone ... > > > > > > Le mar. 20 août 2024, 13:07, Z qiang a écrit : > > > > > > > > > > > > > Hello, Frederic, > > > > > > > > > > I have seen this once on Neeraj's tree with a few commits on top (-rcu > > > > > commit 46774278c74f ("rcutorture: Test start-poll primitives with > > > > > interrupts disabled"). But only the once so far. > > > > > > > > > > This is the WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist)) in > > > > > rcu_nocb_rdp_deoffload(). > > > > > > > > > > Thoughts? > > > > > > > > > > > > > The rcu_segcblist_extract_done_cbs() doesn't reduce the count of > > > > rsclp->len, > > > > in rcu_do_bacth(). this may cause that after we execute the barrier rcu > > > > callback, before decrementing the count of rsclp->len, the rcu_barrier() > > > > returns and makes a judgment of rcu_segcblist_n_cbs(&rdp->cblist) in > > > > rcu_nocb_rdp_deoffload(). > > > > > > > > > > That sounds plausible! You just unlocked my thoughts running in circle > > > since yesterday. > > > > > > > > > > maybe can use WARN_ON_ONCE(rcu_segcblist_n_segment_cbs()) instead > > > > of WARN_ON_ONCE(rcu_segcblist_n_cbs()) > > > > > > > > Thoughts? > > > > > > I'll test that once I'm back from vacation the september 2nd. Thanks! > > > > Thank you both!!! > > > > Running -next over last night hit a number of boot-time splats, so I > > have no idea if this reproduces nicely. Can't have everything! ;-) > > And it is now a two-off given another one last night's testing. This was > from 168 hours of TREE01 on my -rcu "dev" branch (as opposed to -next), > but I have run many runs over the past two weeks. So it is reproducible, > but rare. > > Ah, and if it matters, I synched up to Neeraj's latest as of about 18 > hours ago just before starting this test. Yes, I'm preparing an update for the offending patch (which has one more embarassing issue while I'm going through it again). Thanks.