Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755110AbaJUKKR (ORCPT ); Tue, 21 Oct 2014 06:10:17 -0400 Received: from down.free-electrons.com ([37.187.137.238]:56577 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751023AbaJUKKP (ORCPT ); Tue, 21 Oct 2014 06:10:15 -0400 Date: Tue, 21 Oct 2014 12:10:11 +0200 From: Thomas Petazzoni To: Eric Dumazet Cc: "David S. Miller" , Eric Dumazet , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Alexandre FOURNIER , Ezequiel Garcia , Marcin Wojtas , Gregory =?UTF-8?B?Q2zDqW1lbnQ=?= Subject: Re: RCU stall in af_unix.c, should use spin_lock_irqsave? Message-ID: <20141021121011.53686d5f@free-electrons.com> In-Reply-To: <1413885874.23173.11.camel@edumazet-glaptop2.roam.corp.google.com> References: <20141021100313.397f4962@free-electrons.com> <1413885874.23173.11.camel@edumazet-glaptop2.roam.corp.google.com> Organization: Free Electrons X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.23; 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dear Eric Dumazet, On Tue, 21 Oct 2014 03:04:34 -0700, Eric Dumazet wrote: > > So, the question is: is this patch the correct solution (but then other > > usage of spin_lock in af_unix.c might also need fixing) ? Or is the > > network driver at fault? > > > > Thanks for your input, > > > > Thomas > > Locks in af_unix do not need to mask irqs. Ever. > > skb_queue_tail() uses an irqsave variant because its a generic function, > and _some_ skb list might be manipulated from hard irq handlers in pre > NAPI drivers. But af_unix does not have an interrupt handler that could > potentially try to lock sk_receive_queue.lock Ok. So it's actually safe to mix spin_lock() and spin_lock_irqsave() on the same lock, if you know that this lock will never ever be taken in an interrupt context? > mvpp2 is seriously brain damaged : on_each_cpu() cannot be used from > a bottom half handler. That's what I thought. Back to the drawing board then, to fix mvpp2. Do you think there is a place where we can write down those assumptions? It isn't easy to spot whether on_each_cpu() is safe to use in a bottom half or not. Anyway, thanks a lot for your quick feedback! Best regards, Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/