From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: Re: [PATCH] softirq: Use local_irq_save() in local_bh_enable() Date: Tue, 18 Nov 2008 07:38:19 +0000 Message-ID: <20081118073819.GA4440@ff.dom.local> References: <87y6zwwy5c.fsf@tac.ki.iif.hu> <20081117133548.GC6345@ff.dom.local> <20081117161617.GF12081@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Johannes Berg , David Miller , Ferenc Wagner , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra To: Ingo Molnar Return-path: Received: from fg-out-1718.google.com ([72.14.220.159]:30742 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751201AbYKRHiZ (ORCPT ); Tue, 18 Nov 2008 02:38:25 -0500 Received: by fg-out-1718.google.com with SMTP id 19so2376025fgg.17 for ; Mon, 17 Nov 2008 23:38:23 -0800 (PST) Content-Disposition: inline In-Reply-To: <20081117161617.GF12081@elte.hu> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Nov 17, 2008 at 05:16:17PM +0100, Ingo Molnar wrote: > > * Jarek Poplawski wrote: > > > This report: http://marc.info/?l=linux-netdev&m=122599341430090&w=2 > > shows local_bh_enable() is used in the wrong context (irqs > > disabled). It happens when a usual network receive path is called by > > netconsole, which simply turns off irqs around this all. Probably > > this is wrong, but it worked like this long time, and it's not > > trivial to fix this. > > > > Anyway, a commit 0f476b6d91a1395bda6464e653ce66ea9bea7167 "softirq: > > remove irqs_disabled warning from local_bh_enable" can break things > > after changing from local_irq_save() to local_irq_disable(). Before > > this commit there was only a warning, now a lockup is possible, so > > it could be treated as a regression. This patch reverts the change > > in irqs. > > hm, but calling local_bh_enable() with hardirqs off is a bug. It might > be a long-standing bug, but it can cause lockups even with that change > reverted: when we process softirqs in local_bh_enable(). I think it's what they call a regression: this is a long-standing bug, and this commit doesn't fix this, but can cause additional lockups. > So why not > fix the bug instead? It's not about instead: this bug could be fixed as well (if somebody knows how to do it "properly" without hacks like: if (!in_irq()) local_bh_disable(); etc.; but, I guess, the network code has more such bh disabling). Jarek P.