From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 D5F693D3CEE for ; Wed, 18 Mar 2026 16:47:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773852435; cv=none; b=CMFHGG/uKDetqxcwnkOcCrMLdPcOEH/WrzhjtdymCrVEUwKEc3KYLeqPfhO8vmgyK8yb3xj+UkGsnYhFRYKLrysnkuM61+RPWLVhOjrGUQA1VVHPIf7dfZMqbBIF8cN4japGrTuJiSKfF1QAuy7oBP7kkE2BRQe+17jXpRBtLdQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773852435; c=relaxed/simple; bh=HfpCJhFyj6Y9puS8doHbaugVLDX3X1QFkcADA3vkWCE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mt/S+zAYQbfq72qThPsF7ve9B/2mJU1/3Lxb2Ubp1v030EgO1QHTJysIrIk9bxAbX+t7c8aSIuyBQVtfq5KtDzRqGe6TwJsy8OMwt9u5yu7IK5xIE1021gDgECv48UHa1gltN3cAI+MO32b8JpP2+TGqEj+qUOLGnmqXEqJgZUo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=BQnBFaFF; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=27VysrQ/; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="BQnBFaFF"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="27VysrQ/" Date: Wed, 18 Mar 2026 17:47:10 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1773852431; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aug5CrbJ0rw65zwnvPTMbySmL5KuBdq3cjYZNu0bCkY=; b=BQnBFaFFn0nFTDdncbGDq4ccmmu8vehRrocvhdq8c/wLxj6BSo6PFcVf11LCMw21vSoNjz G9zVtqoCY47eWuDbmd+x/hi7VKJe+QiacNT6RrVkOTHmulBTmORZ9zsK1mgIFYe5rJxhum ZzXxllFhRj5Ph4NLityjP1mdzmZkkFm5AfHHsQWFI1swFCkAXuZ68Oiwd/+K44Y/ArtHrR M0q9ApvIqF7XRqk+A1verfkx7Dojp2ADThMIMTNaPHaepbrRBY3cHOa4dnf24f0WClts55 ufueiWcG1CEghXeT5MXN6ZmUe+q394iOrlWIcBTJGLco09NUExUII+XB00H4tQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1773852431; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aug5CrbJ0rw65zwnvPTMbySmL5KuBdq3cjYZNu0bCkY=; b=27VysrQ/pzGntCvScHARDPIfchRgKyAp8NmxVSIyD0tBszsHuObg1WT0b41lABsu5ymAkf fjF/5SV3sr3b7fDA== From: Sebastian Andrzej Siewior To: "Paul E. McKenney" Cc: frederic@kernel.org, neeraj.iitr10@gmail.com, urezki@gmail.com, joelagnelf@nvidia.com, boqun.feng@gmail.com, rcu@vger.kernel.org, Kumar Kartikeya Dwivedi Subject: Re: Next-level bug in SRCU implementation of RCU Tasks Trace + PREEMPT_RT Message-ID: <20260318164710.gUolNYgg@linutronix.de> References: <20260318105058.j2aKncBU@linutronix.de> <20260318144305.xI6RDtzk@linutronix.de> <76ef9a5e-7343-4b8e-bf3c-cabd8753ecdb@paulmck-laptop> <20260318160445.IyUiWV0T@linutronix.de> <06a0cb91-1737-4691-a810-8340e1acf1d6@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=utf-8 Content-Disposition: inline In-Reply-To: <06a0cb91-1737-4691-a810-8340e1acf1d6@paulmck-laptop> On 2026-03-18 09:32:07 [-0700], Paul E. McKenney wrote: > > What remains? > > With that patch, we no longer have call_srcu() directly acquiring a > non-raw spinlock, but as you say, we still have the wakeup problem. Isn't this is just srcu_funnel_gp_start()? And where you could ensure that it is always a delayed worked (delay always 1+) that is scheduled so that it always setups a timer and never does a direct wake. > > Popular? Okay. Keep me posted, please. > > Will do. Just out of curiosity, what are your concerns? We don't have many NMI code paths and the possibilities are quite dense. I would imagine having this possibility would lead to things that wouldn't be needed otherwise. I mean we don't even allow allocating memory from hardirq (except for _nolock() variant which I think is used by bpf for $reasons) but need to call rcu_free from NMI. This would require to remove an item from some kind of data structure without regular locking. Unless RCU is used to get a delayed invocation of some sorts. I mean I am curious here who needs it any why ;) > Thanx, Paul Sebastian