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 8E9B13C3454 for ; Thu, 19 Mar 2026 10:51:54 +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=1773917515; cv=none; b=t6pamn46pX62tHB2V6/eBp7jNBEB5d+BFB36SYAJrEQQ621UjJ0ciyD9+8jC0r9Mx6gUWra5zDnbBB9e4QQ+lWReyaMAnN1C/3rp77jdLQtej8qc4P+MGGdu1FWakp75+6A6LBrt0HWPg6z5WWINe7bmj14x87utPy1t0LsX3yU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773917515; c=relaxed/simple; bh=SHqC21uTJzVWUAqsZTLf+LBIHXFxu1Nq29JWsvlpFaQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NSIr5gWy0qre6jq6yxNEfOKbXCQ/5ty8zNhzYmRwKRaJ2PJqOZWP2Nmt9dtfoVMUSpLXQCwwRHFyAYizOsUdcsOKZn1e/1V4IT7sSup8OOmhpUEqxvPhqMUAKKL49oKK1zEgdDn4D9bo7c768l2XrieBUqJ1MJ290498Er3bR5w= 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=pg6BSmTa; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Rh/KwtM+; 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="pg6BSmTa"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Rh/KwtM+" Date: Thu, 19 Mar 2026 11:51:51 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1773917513; 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=Og5ICfxwisL/30lO+m4Jglmk8KEbH8GCARAGPI2ZbiM=; b=pg6BSmTaLGSgy8hpwhE41ny/As/aQ3p3/Gw0LEDQtj2bi88HqJOX6A9jKjOt7MWedWn9t1 i5GXW9TCaI9P6A5TtUBFv+APw4RvzCV38SXTGep4pEeXROUBXhs01FKztlqFCIc0x74pEK 2gIx8krnSxWSnQMZscxBadFD0oH3PUYTEBKpot6cFsZxPnnFwDsBbeaYU/BskXV23Frl+q vxF7T0WmXBNn/mFPJqIKkEg07vV9j2zV3EIx8tgpsJ+ZnoG1vxeVGGJXiGoNnGHUtGqwgI s21OqZWwxQXtqGj7NEKleYWXJ6keEoOEYNOq5c9JBJkNVhA/4u5uYOoJ8VyLlA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1773917513; 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=Og5ICfxwisL/30lO+m4Jglmk8KEbH8GCARAGPI2ZbiM=; b=Rh/KwtM+YtxE4UH/oaWTHEFVzmI2TQCxhF0BfDfAvSFsEXRf7/e9bBvQ8mGofEFqrF/WhJ pXI1atyzGtGSezBQ== 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: <20260319105151.Rtzk9nUj@linutronix.de> References: <20260318144305.xI6RDtzk@linutronix.de> <76ef9a5e-7343-4b8e-bf3c-cabd8753ecdb@paulmck-laptop> <20260318160445.IyUiWV0T@linutronix.de> <06a0cb91-1737-4691-a810-8340e1acf1d6@paulmck-laptop> <20260318164710.gUolNYgg@linutronix.de> <9b685d13-5496-4bc9-ab6a-508bd4bf0f16@paulmck-laptop> <20260319085548.UZQk1cyW@linutronix.de> 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: On 2026-03-19 03:43:17 [-0700], Paul E. McKenney wrote: > On Thu, Mar 19, 2026 at 03:05:40AM -0700, Paul E. McKenney wrote: > > On Thu, Mar 19, 2026 at 09:55:48AM +0100, Sebastian Andrzej Siewior wrote: > > > On 2026-03-18 11:48:56 [-0700], Paul E. McKenney wrote: > > > > We would need a lockless enqueue, which we have in llist.h. > > > > > > Only if CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. Otherwise you must not > > > provide call_rcu_nmi(). > > > > I *think* that BPF is provided only in such architectures, so agreed. > > Plus srcu_read_lock_fast() uses atomic_long_inc(), which is supposed to > be NMI-safe anyway, correct? I am not aware of any NMI restrictions for the atomic ops, just cmpxchg. > Thanx, Paul Sebastian