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Thread-Topic: [EXTERNAL] Re: [RFC PATCH 3/4] Hyper-V/Balloon: Call add_memory() with dm_device.ha_lock. Thread-Index: AQHVsDNJjhlisRM1nUS25YM4WFt2Tqe2KWOA Date: Thu, 12 Dec 2019 08:24:18 +0000 Message-ID: References: <20191210154611.10958-1-Tianyu.Lan@microsoft.com> <20191210154611.10958-4-Tianyu.Lan@microsoft.com> <87pnguc3ln.fsf@vitty.brq.redhat.com> In-Reply-To: <87pnguc3ln.fsf@vitty.brq.redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=True; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Owner=tiala@microsoft.com; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2019-12-12T08:24:13.0861288Z; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=General; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Application=Microsoft Azure Information Protection; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=fd7516c9-1daa-4b92-9e4c-17e8a0ab05a2; MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Extended_MSFT_Method=Automatic authentication-results: spf=none (sender IP is ) smtp.mailfrom=Tianyu.Lan@microsoft.com; x-originating-ip: [167.220.255.55] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: d48fe011-8ea1-410a-6a1c-08d77edcaec5 x-ms-traffictypediagnostic: PS1P15301MB0345:|PS1P15301MB0345:|PS1P15301MB0345: x-ms-exchange-transport-forked: True x-ld-processed: 72f988bf-86f1-41af-91ab-2d7cd011db47,ExtAddr x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:2582; x-forefront-prvs: 0249EFCB0B x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(376002)(346002)(396003)(39860400002)(136003)(366004)(199004)(189003)(81166006)(81156014)(8676002)(8936002)(7696005)(10290500003)(71200400001)(6636002)(33656002)(66556008)(64756008)(66946007)(66476007)(52536014)(66446008)(26005)(54906003)(9686003)(110136005)(186003)(8990500004)(478600001)(316002)(55016002)(4326008)(86362001)(5660300002)(6506007)(76116006)(2906002);DIR:OUT;SFP:1102;SCL:1;SRVR:PS1P15301MB0345;H:PS1P15301MB0346.APCP153.PROD.OUTLOOK.COM;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; received-spf: None (protection.outlook.com: microsoft.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 2ps7vlrsb5xBXsbAPoa8Sg+QEurwG4VBr3HAdaPtrjYTwJd7h+/a7f3XBoz9Ku8TKZG7ELq6YUmFO6QHlv0D5knnYQzrhHsG1tmCdPWCQ1OcLlAx3rJTpHMPEhariKIDm7K+fgyuDStaMo6OLBZnLVAgCnnK8Orlt8dr1uUQzEhaysdxLgONk3jlqqIBkNxG7I6azvk5rvGTcoYVdSnmmKtA/1AAoUZglf+2aiEYixypZJRILbrxCTkFBEgif1yC17y3mfrfkD0YmhmeZzkcDvxn1yCBh9T/97RJVw5lkSvPa1B6brdbu1jUi6S1KL+hDyeghwBxH2bo+rlDiWfUaE2ZGQ3hvUW7x8dP2TO9o+rm5Qlm70dK0ZUhoTc2BluSXEcesOZq6HZnQ+sTRa+vJDs/IFRZwnQPmiRPhBYxNEcy8/m+NXOgpSoMm8LGTCXP Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: d48fe011-8ea1-410a-6a1c-08d77edcaec5 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Dec 2019 08:24:18.2355 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: imjxGrHBLF6S2++oQaNHVOhZj81n5WBHuVAuurkQuzui1bcaReROZvRZmPxaefZ2ATE/8tS/DrXYNeNoBwFqqA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PS1P15301MB0345 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vitaly: Thanks for your review. > From: Vitaly Kuznetsov =20 > > From: Tianyu Lan > > @@ -771,8 +767,13 @@ static void hv_online_page(struct page *pg, > unsigned int order) > > struct hv_hotadd_state *has; > > unsigned long flags; > > unsigned long pfn =3D page_to_pfn(pg); > > + int unlocked; > > + > > + if (dm_device.lock_thread !=3D current) { >=20 > With lock_thread checking you're trying to protect against taking the spi= nlock > twice (when this is called from add_memory()) but why not just check that > spin_is_locked() AND we sit on the same CPU as the VMBus channel > attached to the balloon device? Yes, that's another approach. >=20 > > + spin_lock_irqsave(&dm_device.ha_lock, flags); > > + unlocked =3D 1; > > + } >=20 > We set unlocked to '1' when we're actually locked, aren't we? The "unlocked" means ha_lock isn't hold before calling hv_online_page(). >=20 > > > > - spin_lock_irqsave(&dm_device.ha_lock, flags); > > list_for_each_entry(has, &dm_device.ha_region_list, list) { > > /* The page belongs to a different HAS. */ > > if ((pfn < has->start_pfn) || > > @@ -782,7 +783,9 @@ static void hv_online_page(struct page *pg, > unsigned int order) > > hv_bring_pgs_online(has, pfn, 1UL << order); > > break; > > } > > - spin_unlock_irqrestore(&dm_device.ha_lock, flags); > > + > > + if (unlocked) > > + spin_unlock_irqrestore(&dm_device.ha_lock, flags); > > } > > > > static int pfn_covered(unsigned long start_pfn, unsigned long > > pfn_cnt) @@ -860,6 +863,7 @@ static unsigned long > handle_pg_range(unsigned long pg_start, > > pg_start); > > > > spin_lock_irqsave(&dm_device.ha_lock, flags); > > + dm_device.lock_thread =3D current; > > list_for_each_entry(has, &dm_device.ha_region_list, list) { > > /* > > * If the pfn range we are dealing with is not in the current > @@ > > -912,9 +916,7 @@ static unsigned long handle_pg_range(unsigned long > pg_start, > > } else { > > pfn_cnt =3D size; > > } > > - spin_unlock_irqrestore(&dm_device.ha_lock, flags); > > hv_mem_hot_add(has->ha_end_pfn, size, pfn_cnt, > has); > > - spin_lock_irqsave(&dm_device.ha_lock, flags); >=20 > Apart from the deadlock you mention in the commit message, add_memory > does lock_device_hotplug()/unlock_device_hotplug() which is a mutex. If > I'm not mistaken you now take the mutext under a spinlock > (&dm_device.ha_lock). Not good. Yes, you are right. I missed this. I will try other way. Nice catch. Thanks= . >=20 >=20 > > } > > /* > > * If we managed to online any pages that were given to us, > @@ > > -923,6 +925,7 @@ static unsigned long handle_pg_range(unsigned long > pg_start, > > res =3D has->covered_end_pfn - old_covered_state; > > break; > > } > > + dm_device.lock_thread =3D NULL; > > spin_unlock_irqrestore(&dm_device.ha_lock, flags); > > > > return res; >=20 > -- > Vitaly