From owner-freebsd-hackers@FreeBSD.ORG Thu Jul 11 21:20:36 2013 Return-Path: Delivered-To: hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 51C06A8E for ; Thu, 11 Jul 2013 21:20:36 +0000 (UTC) (envelope-from toasty@dragondata.com) Received: from mail-gg0-x232.google.com (mail-gg0-x232.google.com [IPv6:2607:f8b0:4002:c02::232]) by mx1.freebsd.org (Postfix) with ESMTP id 0E52416B9 for ; Thu, 11 Jul 2013 21:20:35 +0000 (UTC) Received: by mail-gg0-f178.google.com with SMTP id l12so2889538gge.9 for ; Thu, 11 Jul 2013 14:20:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dragondata.com; s=google; h=content-type:mime-version:subject:from:in-reply-to:date:cc :message-id:references:to:x-mailer; bh=G+GmsOc2/l1TQLXLGb6+KWXNcM7sWN7uKeMQeQoTOjw=; b=PEZ8nn0OsE5YQTS5G1zOjiWGOQxYW4SRLUUCr0uBc2r04aw0VmZTI0i6mCxdeRUq9B KQuCp5J2dGldlFuuB4m+yO3xyZIauBGraWHyv7ij1Teosdej0wan5wPWwPvfKJFFL2Ti 0J3FVsoiiFUmNSBVEf20OQ4S1v+LA8nTIhlUs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=content-type:mime-version:subject:from:in-reply-to:date:cc :message-id:references:to:x-mailer:x-gm-message-state; bh=G+GmsOc2/l1TQLXLGb6+KWXNcM7sWN7uKeMQeQoTOjw=; b=Pi37AU/fxv+Cyy3AZQD09LouBFD71RzkTkDH3T87ZIWonCbRXxhwF01nPkcEeE4wNn n4vi0OYgu67GM/eQwMNXIBFKWFuocGKAqtZBzrZVd+A0R2rDPCe1Q6mtLT8OCXJ2+ZLq r8bC8zabPOM9Ca/He+kzOhLjEDbfMV70IvW3yNLuhIlXQUT59Z1ai+kUul5lzw8sdL4m nlnMLEyMFefclj5xsaYmRlytC8SCpWiTelOPh9GaZn9cbum5b00DCgmlSiIBqUmkvQCW EEUMlApxFSGBx1qGt9xBFs6l9kMuEPQbeSGFdgUt+NGjLgjlNtrzDAS6IFokeQ6BjxZ5 RobQ== X-Received: by 10.236.161.3 with SMTP id v3mr21982090yhk.3.1373577635544; Thu, 11 Jul 2013 14:20:35 -0700 (PDT) Received: from unassigned.v6.your.org ([2001:4978:1:45:c937:933:fe02:226a]) by mx.google.com with ESMTPSA id h26sm62849823yhb.21.2013.07.11.14.20.33 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 11 Jul 2013 14:20:34 -0700 (PDT) Content-Type: multipart/signed; boundary="Apple-Mail=_17B5C70A-9C60-4DFA-A1CF-40315A6880DB"; protocol="application/pkcs7-signature"; micalg=sha1 Mime-Version: 1.0 (Mac OS X Mail 6.5 \(1508\)) Subject: Re: Kernel dumps [was Re: possible changes from Panzura] From: Kevin Day In-Reply-To: Date: Thu, 11 Jul 2013 16:20:32 -0500 Message-Id: References: <9890DFF1-892A-4DCA-9E33-B70681154F43@mail.turbofuzz.com> <4F0DFAB7-D6D5-4068-A543-C9DF885D1A7D@dragondata.com> <51DEC0E8.7010305@freebsd.org> To: Artem Belevich X-Mailer: Apple Mail (2.1508) X-Gm-Message-State: ALoCoQl2GR7aoNnrsh6H3WydmrMzMCaKqHI8rbMAsdoJ8Wo6NQgm5syu5vHexO2+iBUQ5H4BHWoO Cc: hackers@freebsd.org, "Jordan K. Hubbard" X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 11 Jul 2013 21:20:36 -0000 --Apple-Mail=_17B5C70A-9C60-4DFA-A1CF-40315A6880DB Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=iso-8859-1 On Jul 11, 2013, at 4:05 PM, Artem Belevich wrote: > =20 > It would probably work for most of the crashes, but will not work in = few interesting classes of failure. Using in-kernel stack implicitly = assumes that your memory allocator still works as both the stack and the = interface driver will need to get their mbufs and other data somewhere. = Alas it's those unusual cases that are hardest to debug and where you = really do want debugger or coredump to work. >=20 > Back at my previous work we did it 'embedded system way'. Interface = driver provided dumb functions to re-init device, send a frame and poll = for received frame. All that without using system malloc. There was a = dumb malloc that gave few chunks of memory from static buffer to gzip, = but the rest of the code was independent of any kernel facilities. We = had simple ARP/IP/UDP/TFTP(+gzip) implementation to upload compressed = image of physical memory to a specified server. Overall it worked pretty = well. That's the exact reason why we invented our own mini stack and hooks = into the network driver. After many failure cases, you can no longer = rely on malloc, interrupts, routing tables or other goodies to be = working correctly. It's too easy for the rest of the system to be broken = enough that touching any of those pieces was enough to crash again. It really depends on the scope of problem you're trying to debug, but at = minimum I think you need to revert to polled networking, disable all = interrupts, and use your own stack/memory pool. Even then it's still not = foolproof, but at least then you spend less time trying to debug your = debugger. --Apple-Mail=_17B5C70A-9C60-4DFA-A1CF-40315A6880DB Content-Disposition: attachment; filename=smime.p7s Content-Type: application/pkcs7-signature; name=smime.p7s Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIPLzCCBN0w ggPFoAMCAQICEHGS++YZX6xNEoV0cTSiGKcwDQYJKoZIhvcNAQEFBQAwezELMAkGA1UEBhMCR0Ix GzAZBgNVBAgMEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBwwHU2FsZm9yZDEaMBgGA1UECgwR Q29tb2RvIENBIExpbWl0ZWQxITAfBgNVBAMMGEFBQSBDZXJ0aWZpY2F0ZSBTZXJ2aWNlczAeFw0w NDAxMDEwMDAwMDBaFw0yODEyMzEyMzU5NTlaMIGuMQswCQYDVQQGEwJVUzELMAkGA1UECBMCVVQx FzAVBgNVBAcTDlNhbHQgTGFrZSBDaXR5MR4wHAYDVQQKExVUaGUgVVNFUlRSVVNUIE5ldHdvcmsx ITAfBgNVBAsTGGh0dHA6Ly93d3cudXNlcnRydXN0LmNvbTE2MDQGA1UEAxMtVVROLVVTRVJGaXJz dC1DbGllbnQgQXV0aGVudGljYXRpb24gYW5kIEVtYWlsMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A MIIBCgKCAQEAsjmFpPJ9q0E7YkY3rs3BYHW8OWX5ShpHornMSMxqmNVNNRm5pELlzkniii8efNIx 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