From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755536AbbJ1HOj (ORCPT ); Wed, 28 Oct 2015 03:14:39 -0400 Received: from casper.infradead.org ([85.118.1.10]:35748 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752101AbbJ1HOh (ORCPT ); Wed, 28 Oct 2015 03:14:37 -0400 Message-ID: <1446016471.3405.201.camel@infradead.org> Subject: [PATCH] Document that IRQ_NONE should be returned when IRQ not actually *handled* From: David Woodhouse To: linux-kernel@vger.kernel.org, tglx@linutronix.de, davem@davemloft.net Date: Wed, 28 Oct 2015 16:14:31 +0900 Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-pUOA2fd/V/RDat5brRj9" X-Mailer: Evolution 3.16.5 (3.16.5-3.fc22) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-pUOA2fd/V/RDat5brRj9 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Our IRQ storm detection works when an interrupt handler returns IRQ_NONE for thousands of consecutive interrupts in a second. It doesn't hurt to occasionally return IRQ_NONE when the interrupt is actually genuine. Drivers should only be returning IRQ_HANDLED if they have actually *done* something to stop an interrupt from happening =E2=80=94 it doesn't j= ust mean "this really *was* my device". Signed-off-by: David Woodhouse --- See recent discussion about the 8139cp Ethernet driver=C2=B9. It developed (OK, I introduced) a bug where it would re-enable the RX IRQ when handling a TX timeout and resetting the hardware. This leads to an IRQ storm with cp_interrupt() *not* doing anything about the RX IRQ, because NAPI was already scheduled. And then returning IRQ_HANDLED anyway. And complete death of the machine. Our IRQ storm detection should handle that kind of thing =E2=80=94 it's designed to catch both hardware *and* software screwups. But because of the cp_interrupt() return value, it didn't. I tried to fix cp_interrupt(), and submitted a patch which made the failure mode much saner =E2=80=94 the offending IRQ got disabled and the machine continued happily, with the network even *working* in polling mode. It met with resistance. To overcome that resistance, we should clearly document the expectation that device drivers should return IRQ_NONE in that kind of case. Let's start by at least fixing the *wrong* text in irqreturn.h, which says that IRQ_NONE means "not my device"... =C2=B9 http://www.spinics.net/lists/netdev/msg343991.html http://www.spinics.net/lists/netdev/msg343995.html http://www.spinics.net/lists/netdev/msg344265.html diff --git a/include/linux/irqreturn.h b/include/linux/irqreturn.h index e374e36..eb1bdcf 100644 --- a/include/linux/irqreturn.h +++ b/include/linux/irqreturn.h @@ -3,7 +3,7 @@ =20 /** * enum irqreturn - * @IRQ_NONE interrupt was not from this device + * @IRQ_NONE interrupt was not from this device or was not handled * @IRQ_HANDLED interrupt was handled by this device * @IRQ_WAKE_THREAD handler requests to wake the handler thread */ --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-pUOA2fd/V/RDat5brRj9 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 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