From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: 2.6.23-rc2: WARNING: at kernel/irq/resend.c:70 check_irq_resend() Date: Fri, 10 Aug 2007 11:33:53 +0200 Message-ID: <20070810093353.GA19777@elte.hu> References: <18107.11431.838905.331157@stoffel.org> <20070809155445.GA5161@ff.dom.local> <1186733140.12828.45.camel@chaos> <20070810082346.GD1764@ff.dom.local> <20070810083050.GA4545@elte.hu> <20070810084924.GF1764@ff.dom.local> <20070810085611.GA11639@elte.hu> <20070810091231.GH1764@ff.dom.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Thomas Gleixner , John Stoffel , linux-kernel@vger.kernel.org, shemminger@linux-foundation.org, vignaud@xandmail.fr, marcin.slusarz@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, linux-net@vger.kernel.org, netdev@vger.kernel.org To: Jarek Poplawski Return-path: Received: from mx2.mail.elte.hu ([157.181.151.9]:49137 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753211AbXHJJeL (ORCPT ); Fri, 10 Aug 2007 05:34:11 -0400 Content-Disposition: inline In-Reply-To: <20070810091231.GH1764@ff.dom.local> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org * Jarek Poplawski wrote: > > > > + } > > > > #ifdef CONFIG_HARDIRQS_SW_RESEND > > > > we used the hw-resend method unconditionally, right? > > Right: unconditionally on a condition they are not edges... > > But, since not resending at all seems to work so good in testing, I > thought, _SW_RESEND could be considered as an unnecessarily > complicated alternative. > > Now, I'm a bit confused... the idea is multi-pronged: - Primarily, we want to fix the regression. 2.6.20 worked, 2.6.21 didnt, that has to be fixed, no matter what - end of story. But we've got a wide selection of patches for that purpose now, so what matters at this point is the secondary question: - we want to know _why exactly_ the hang happens. We now have a pretty good theory: hw-resend hangs the IO-APIC. (there is a delicate dance between local APICs and IO-APICs for level-triggered irqs, and if we interject via hw-resending via the local APIC, existing races, hw bugs or weaknesses in our hw-resend implementation might be exposed) and even though we now have a wide selection of patches we really want to get to the bottom of the problem so that we can fix the bug that got exposed: apparently hw resend doesnt always work with level-triggered irqs. Note that the hw-resend sequence can trigger _even without our original patch that triggered the regression_, it's just much less likely to happen, so this is a pre-existing IO-APIC/APIC code bug that could trigger anytime, and which we want to see fixed. To confirm this theory - does the debug-patch below fix the hang? If it fixes the hang then the theory is confirmed and then the right solution is to retrigger an IRQ for level-triggered irqs with the proper trigger-type set. Ingo ------------------> Not-Signed-off-by: Ingo Molnar Index: linux/arch/i386/kernel/io_apic.c =================================================================== --- linux.orig/arch/i386/kernel/io_apic.c +++ linux/arch/i386/kernel/io_apic.c @@ -735,7 +735,8 @@ void fastcall send_IPI_self(int vector) * Wait for idle. */ apic_wait_icr_idle(); - cfg = APIC_DM_FIXED | APIC_DEST_SELF | vector | APIC_DEST_LOGICAL; + cfg = APIC_DM_FIXED | APIC_DEST_SELF | vector | APIC_DEST_LOGICAL | + APIC_INT_LEVELTRIG; /* * Send the IPI. The write to APIC_ICR fires this off. */