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d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=huxai53Bc2Yv6lid00KRVR3RcUa5n3pg3mqGq6v7ZI4=; b=gtY3VyJVlIdIw4w8tDlt7oBoXmctryE+gGoOeogzSUkb86jJna7SlaCDfawn9qVINYF9a+ZmW8LjyTphZoitpVR+eutEEt3hvS3rG/r0ge4KIJO+z5aZKX/Quv78c5NkROtHPYWzdA9Cp883gqeqOHU+szwVECCqQzCd0pWI/53GrvpDULCDuN/F4u7FkK6FyqwZ67R5dp4ymPI6KztLJ9yEjnRDkm3x064AemnpKFGmS/bSjmYv4nRFkvgEDwkb9lOrR9d/qcVLug5k1y+Hj6+K9DSAr1MS+mm4hIz0GumUq7cCjGfvc9maYM4DUstn0C66/9qaDZbL4OdhceXCvA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=suse.com; dmarc=pass action=none header.from=suse.com; dkim=pass header.d=suse.com; arc=none From: Dario Faggioli To: "julien@xen.org" , "ahmeddan@amazon.co.uk" , "xen-devel@lists.xenproject.org" CC: "sstabellini@kernel.org" , "mpohlack@amazon.de" , "jgrall@amazon.co.uk" , "doebel@amazon.de" Subject: Re: NULL scheduler DoS Thread-Topic: NULL scheduler DoS Thread-Index: AQHXjTpOV/XWdF2YLUCIZdYgL03Tzatrb1sAgAAzUoCAAnTJAA== Date: Wed, 11 Aug 2021 10:09:25 +0000 Message-ID: <6b5e28f427ccd89505a4448f2b9e5be992a08292.camel@suse.com> References: <8193a685-3ab1-9407-75f3-e335ea4406e4@xen.org> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: user-agent: Evolution 3.40.3 (by Flathub.org) authentication-results: xen.org; 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micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-niKy73NtsCz6729M72v8" MIME-Version: 1.0 X-OriginatorOrg: suse.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: AM0PR04MB5826.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0944db32-45b1-41ad-b707-08d95cb01926 X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Aug 2021 10:09:25.5133 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: eH8ke4W5extcJwZTEhsXajBLRn46ysdvbKs1Kb/JtqGzHYXnGF7da7wACIGSQ8lavyayGJxXkl6WclA13mrJ1A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM9PR04MB8193 --=-niKy73NtsCz6729M72v8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2021-08-09 at 21:38 +0100, Julien Grall wrote: > On 09/08/2021 18:35, Julien Grall wrote: > >=20 > > This implies that a pCPU may temporarily be assigned to two vCPUs > > and we=20 > > expect to be fixed up afterwards. However, a domain may be > > destroyed=20 > > before this is happening. > >=20 > > So it looks like that unit_deassign() is not able to cope with this > > case. From a brief look, I think we may want to check if the pCPU > > is in=20 > > the wait list. If it is, then we should bail out. >=20 > Actually, I was wrong. It looks like null_unit_remove() is already=20 > checking this condition. Also, the vCPU should be offline (and the > unit=20 > as well) because they haven't come online yet: >=20 That's what is currently puzzling me. I mean, the crash happens in unit_deassign(), called by null_unit_remove(), called by sched_destroy_vcpu(). And I agree that the unit should be offline, but null_unit_remove() calls unit_deassign() only if the unit *is* online, so... What's going on? :-/ Regards --=20 Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <> (Raistlin Majere) --=-niKy73NtsCz6729M72v8 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEES5ssOj3Vhr0WPnOLFkJ4iaW4c+4FAmETodQACgkQFkJ4iaW4 c+7kLA/+MAi8knfYmFGabyS6hOODKRMl9O/Iqnevl9uvOTte+ltRsrRtEufdd2uu wmFd346vgSTRqOPBSNvzbs9/7m8lHwRXlKJZW6dICWRKXHcK6052iEYfst4zvOBF avpuKRfW/v8Me3ryoNI3efkC4QZU01XPY71KDLNUZ8Tz+ro3iY2QdYeggL1V6x0z z7ByyDzHwjkLQT0ckhEClCHcqyQ9rCJdtkJbXdkxP8hUg7S6WyIJxV6PPqrrKkFl MfTdfKZrM4BP3/hIsLNRF+mpAnZJ3/VlNu0ofVmlzw4YsP5jhH2iZxLQpsiFTZ8u to2ImLXW5JI4zGWACH8wGN/12pbg64x//Gw3mrkvFQ2Ywhjn2okJ6NE2NKwVu39l A69dUfMY4mm+xhKgXOOMCMvXHfJEC+PPLFcV1LCVhfBor/0sZaECnzT1H4sLX5u8 0Cx6oyIcWqaxRIo2eo4W9KYwXIZXJlnivl+meyj66ZCf/wZXV5LljZjeILPvhhCP 0vaFlURwDmh8Q/V4JkqMXG3mZJE7U/560luWgqyL6nEjjxqztAqUV8Xbhqs2nR3/ miuyYQLRXlfgW2IIvWsjWOAmWF/f1NxzE62x65T1sMtt6aX/W7SxCnBCi6Luq2xa yHk/L4MknrGu8ULWpRX0Jy5U/6xnn92oK3QyMQWdRK9CN8D1TOk= =3H5I -----END PGP SIGNATURE----- --=-niKy73NtsCz6729M72v8--