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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 842f08ca-d3f0-4934-6c32-08d73e65089e X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Sep 2019 07:26:34.9885 (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: G8yRhLUbZ+FmakY97HX6wfRPUGfSWe+AO+bAz61sB82TwYeKwpEzurzxvs0M45OKmWxtPqlnd95je2caW+bUhw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PU1P153MB0122 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org > From: Vitaly Kuznetsov > Sent: Thursday, September 19, 2019 3:28 AM >=20 > Dexuan Cui writes: >=20 > > BTW, for vss, maybe the VM should not hibernate if there is a backup > > ongoing? -- if the file system is frozen by hv_vss_daemon, and the VM > > hibernates, then when the VM resumes back, it's almost always true that > > the VM won't receive the host's VSS_OP_THAW request, and the VM will > > end up in an unusable state. >=20 > Makes sense. Or, alternatively, can we postpone hibernation until after > VSS_OP_THAW? >=20 > Vitaly It looks we should not postpone that, because: 1. When we're in util_suspend(), all the user space processes have been frozen, so even if the VM receives the VSS_OP_THAW message form the host, there is no chance for the hv_vss_daemon to handle it.=20 2. Between the window the host sends the VSS_OP_FREEZE message and the VSS_OP_THAW mesasge, util_suspend() may jump in and close the channel, and then the host will not send a VSS_OP_THAW. 3. The host doesn't guarantee how soon it sends the VSS_OP_THAW message, though in practice IIRC the host *usually* sends the message soon. The hibernation process has a watchdog of 120s set by dpm_watchdog_set(): if dpm_suspend() (which calls util_probe()) can not finish in 120 seconds, the hibernation will be aborted. 3 may not look like a strong reason, but generally speaking I'd like to avo= id an indeterminate dependency. Thanks, -- Dexuan