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Thread-Topic: [PATCH] KVM: Fix an issue in non-preemptible kernel. Thread-Index: AQHVYylkk5V28nmdRkmNneMu0zLGcA== Date: Wed, 4 Sep 2019 14:02:30 +0000 Message-ID: <20190904135343.gbqfs4nlpnjvyfhc@pburton-laptop> References: <20190902090148.10356-1-qfu@wavecomp.com> In-Reply-To: <20190902090148.10356-1-qfu@wavecomp.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: LO2P265CA0289.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a5::13) To MWHPR2201MB1277.namprd22.prod.outlook.com (2603:10b6:301:18::12) user-agent: NeoMutt/20180716 authentication-results: spf=none (sender IP is ) smtp.mailfrom=pburton@wavecomp.com; x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [94.196.178.126] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 0ac7b58c-29f9-400b-575b-08d731408676 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(7168020)(4627221)(201703031133081)(201702281549075)(8990200)(5600166)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR2201MB1485; x-ms-traffictypediagnostic: MWHPR2201MB1485: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6790; x-forefront-prvs: 0150F3F97D x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(7916004)(136003)(366004)(396003)(376002)(39840400004)(346002)(199004)(189003)(51914003)(476003)(386003)(6506007)(53936002)(14454004)(42882007)(446003)(11346002)(186003)(486006)(102836004)(71190400001)(71200400001)(1076003)(9686003)(6512007)(55236004)(478600001)(4326008)(33716001)(2906002)(6862004)(6486002)(25786009)(66066001)(6246003)(6436002)(99286004)(26005)(44832011)(8676002)(7736002)(76176011)(256004)(14444005)(66946007)(229853002)(66476007)(305945005)(66446008)(64756008)(66556008)(52116002)(58126008)(81156014)(8936002)(81166006)(316002)(5660300002)(54906003)(6116002)(3846002);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR2201MB1485;H:MWHPR2201MB1277.namprd22.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; received-spf: None (protection.outlook.com: wavecomp.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: pm7yEJ5LkW0n/3rwfcWJmx9s42ICVtYDc468f2+b2GrGPc2L1pfMiwOq6pr1MvYitOabv3QbH3Q4eQonNu6MyW0Qn+4lDhasXEgGAewDKU3lY4L5y4xNwHi5ZZp2xNnjmq/0r5VEhleeEggGfa6fOQu0A4wgZRPIdTLMIpWJ16VVttWRq08IrRCHYKYRPMB7G41j6WiI7B/pV/JVmSixvTlKMNzIue2rg7K/Zn/Vpxsad6f7eNYaoowqAU8hMgP0i8GUSvjvJzOEGvfs0yg8ACLON935u1v4KoYVo1eWM0XUCpd7wZmr1ZD3tgSJlBqC25BzbpWhh9YD0zjnCuqAjxb5b3PxTX47AKQ3+lS3YCgsOaqTG0EYMg0tl1ysj4raKNDR+bq+tOJ1cRzDCTulor+QV9NuIXjyDjrb2Z3+52o= Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: mips.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0ac7b58c-29f9-400b-575b-08d731408676 X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Sep 2019 14:02:30.4013 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 463607d3-1db3-40a0-8a29-970c56230104 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 2Fn5SznhqjVjvyuNuwYV2e+xtBAssU918pH2TAnQzuQNi8TOuGK9qWgHtDTT1iFc5+4kCU8kkuAy6Ea3fMAJlw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR2201MB1485 Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi Gary, On Mon, Sep 02, 2019 at 09:02:32AM +0000, Gary Fu wrote: > Add a cond_resched() to give the scheduler a chance to run madvise > task to avoid endless loop here in non-preemptible kernel. Thanks for the patch! > Otherwise, the kvm_mmu_notifier would have no chance to be descreased s/descreased/decreased/ (and in the comment too) > to 0 by madvise task -> syscall -> zap_page_range -> > mmu_notifier_invalidate_range_end -> > __mmu_notifier_invalidate_range_end -> invalidate_range_end -> > kvm_mmu_notifier_invalidate_range_end, as the madvise task would be > scheduled when running unmap_single_vma -> unmap_page_range -> > zap_p4d_range -> zap_pud_range -> zap_pmd_range -> cond_resched which > is called before mmu_notifier_invalidate_range_end in zap_page_range. I'm not entirely sure I follow - could you clarify whether the task invoking the madvise syscall is related to the task using KVM? > Signed-off-by: Gary Fu > --- > arch/mips/kvm/mmu.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) >=20 > diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c > index 97e538a8c1be..e52e63d225f4 100644 > --- a/arch/mips/kvm/mmu.c > +++ b/arch/mips/kvm/mmu.c > @@ -746,6 +746,22 @@ static int kvm_mips_map_page(struct kvm_vcpu *vcpu, = unsigned long gpa, > */ > spin_unlock(&kvm->mmu_lock); > kvm_release_pfn_clean(pfn); > + /* > + * Add a cond_resched() to give the scheduler a chance to run > + * madvise task to avoid endless loop here in non-preemptible > + * kernel. > + * Otherwise, the kvm_mmu_notifier would have no chance to be > + * descreased to 0 by madvise task -> syscall -> zap_page_range > + * -> mmu_notifier_invalidate_range_end -> > + * __mmu_notifier_invalidate_range_end -> invalidate_range_end > + * -> kvm_mmu_notifier_invalidate_range_end, as the madvise task > + * would be scheduled when running unmap_single_vma -> > + * unmap_page_range -> zap_p4d_range -> zap_pud_range -> > + * zap_pmd_range -> cond_resched which is called before > + * mmu_notifier_invalidate_range_end in zap_page_range. > + */ > + if (need_resched()) > + cond_resched(); Can we remove the need_resched() check here? cond_resched() already checks should_resched(0) which tests the same thread-info flag as need_resched(). So we should be fine to just call cond_resched() unconditionally. Thanks, Paul > goto retry; > } > =20 > --=20 > 2.17.1 >=20