From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id E5ADE8FC for ; Wed, 27 Jul 2016 00:03:14 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 61C3B162 for ; Wed, 27 Jul 2016 00:03:14 +0000 (UTC) Message-ID: <1469577784.120686.373.camel@infradead.org> From: David Woodhouse To: Andy Lutomirski Date: Wed, 27 Jul 2016 01:03:04 +0100 In-Reply-To: References: <20160719034717.GA24189@swordfish> <535ebaec-1653-3077-d17b-feb847fd51d2@suse.com> <578EF192.3050808@huawei.com> <028967b8-6107-9d9c-453a-a7f25e967f70@suse.com> <1469097065.120686.124.camel@infradead.org> <1469544015.120686.324.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-6O8gU29RKowGcv7l9efK" Mime-Version: 1.0 Cc: "ksummit-discuss@lists.linuxfoundation.org" Subject: Re: [Ksummit-discuss] [TECH TOPIC] asynchronous printk List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-6O8gU29RKowGcv7l9efK Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2016-07-26 at 14:00 -0700, Andy Lutomirski wrote: >=20 > >> But doing this really nicely does tie in to the async printk > >> discussion for a different reason.=C2=A0 I think that we should always > >> initialize the obvious "early" consoles that can be cleanly enumerated > >> early (e.g. EFI).=C2=A0 What we shouldn't do by default is *display* > >> anything to them unless we crash, because the distro people want a > >> clean boot to look pretty.=C2=A0 ISTM the condition for flushing the a= sync > >> printk buffers could be the same as the condition for actually writing > >> to pre-VT consoles. > > > > Me no like. > > > > That makes even *less* sense for early boot than it does during later > > runtime. Because even *more* of the 'we crash' scenarios during early > > boot are going to be uncontrolled "oh shit" happenings, not "oh dear, > > it looks like we're going to crash so let's helpfully dump out all the > > console messages before we do so". >=20 > I only meant in the cases where we're currently silent.=C2=A0 If we boot > with "quiet" and we panic, couldn't we at least try to flush out the > printk buffer onto the early console?=C2=A0 Currently we just sit there > with a blank screen.=C2=A0 (I debugged a case exactly like that last week= .) Sure, *that* part makes some sense if we can work out the details. One of the issues is that you can end up with out-of-order messages =E2=80= =94 for example if you've already printed everything above KERN_CRIT as it happened, and you then go back and re-print the *whole* logbuffer when you realise you're going to panic. If you *haven't* actually printed any lines yet then that's kind of OK, but are you really intending to keep track of that and behave differently if you have? And if you spew *everything* on panic to a limited output like the bootx or VGA text-mode console, you might find that the KERN_DEBUG messages obscure what actually happened, which would be visible if you only printed KERN_NOTICE and above... so maybe the best option is just to honour the loglevel on the command line, but to do it *early*. Heuristics for 'dump the logbuffer when you panic' still aren't a panacea. --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-6O8gU29RKowGcv7l9efK Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEeAw ggXiMIIDyqADAgECAhBrp4p9CteI1lEK+Vnk57ThMA0GCSqGSIb3DQEBCwUAMH0xCzAJBgNVBAYT AklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0 aWZpY2F0ZSBTaWduaW5nMSkwJwYDVQQDEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTAeFw0xNTEyMTYwMTAwMDVaFw0zMDEyMTYwMTAwMDVaMHUxCzAJBgNVBAYTAklMMRYwFAYDVQQK Ew1TdGFydENvbSBMdGQuMSkwJwYDVQQLEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTEjMCEGA1UEAxMaU3RhcnRDb20gQ2xhc3MgMSBDbGllbnQgQ0EwggEiMA0GCSqGSIb3DQEBAQUA A4IBDwAwggEKAoIBAQC9fdr3w6J9g/Zbgv3bW1+uHht1wLUZr5gkrLtXedg17AkefMyUGwrQdvwO 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