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mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=LjZN2yR43dGRx39ih2tx5i2/Ql+3p+wJnVZbqSFLIdY=; b=kt/lv+zY5S7BJBByeOeX0QvPjzmfXjD7Q+0WQKudsCvOqNO/gVCe5fRJXtyZR4frwcqpu+cgsonHaIzsVgBInHaqDi0xmZbqYzif7RWCbMDxGuKEYmwkLQGTz69GDePkDJhxNvlNbDU/7kFOoWHpOCnm1nuOD28aUSCXssC8t2M= Subject: Re: BUG in 1f3d87c75129 ("x86/vpt: do not take pt_migrate rwlock in some cases") To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Jan Beulich CC: Igor Druzhinin , , , References: <0efd0099-49bb-e20c-fe8d-fb97c9de2b63@citrix.com> <74378af9-5d04-f95e-3957-918cf5c81ded@suse.com> <3e9f4ea8-2fca-bf66-6345-0b73b960cba7@suse.com> From: Andrew Cooper Message-ID: <3aaed845-b273-0688-4cac-3d440e3d58d3@citrix.com> Date: Tue, 15 Jun 2021 10:17:24 +0100 User-Agent: Mozilla/5.0 (X11; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?QlJkdFVOVXBLVC8rY2tMMXA3VHlxcUUzZVc5R0FyLzRGblA4RVduYjhtdElW?= =?utf-8?B?dzVucml1dkxtMVJyazg4MjIrdkNUSUc5dlZjNUR2QnVZMDBKVXozZVcrMWdO?= =?utf-8?B?aURwTDNHSEpqUjhyZDU0eVRJbmJWMDdkV3RkNWxrTEk3aCt2eUhhN0VFRDNL?= =?utf-8?B?cVhSOXIwaEJyLzlIbTVhUERzSDAvcVlXZElRMGlJUHh2d0FSSENMVHYvWGFh?= =?utf-8?B?bEVaYUpsdGRLeWZzbVY1bVlvMXY3TEpYK0lpdUZjQnJZREgxKzhLajdiQ0pj?= =?utf-8?B?UkQxYTFOZmxrQjhjS2lJSGxkbFZNNzRLVWczYUxzbU5MQmxRRVU4WkdtRUNi?= =?utf-8?B?WlJMdUZuUkphOUFIRzY5bDVHVlNiOUdYL1FrU2xlN1dJZjlZMG5wMHduWFp5?= =?utf-8?B?bWlpa2VsVFpSakdiaWpSOHJhSW5kaW5RVVNHOEczc1lyMWRhYW8yQWlkTk5a?= =?utf-8?B?d2RNc1pUZUlxNzZLZE1CTFRqNGxtTHBzcVJhSDdiNllRVEhRanF5QXRXTW1p?= =?utf-8?B?b0IxMTFqZmg3MDcrOUNabXRaMU9OeWN0dFhaSi8xL0FUcFJDTVE3c25EQXdZ?= =?utf-8?B?b2RvaVFaRERPeXk1T2ZPeExwMUsvcVBvWkxrYzBNOHoyZmkzQW02Q0lacFQ0?= =?utf-8?B?ZHV0YWpadzdDQXE5dE1jOVdHZ0hHOWRjRUkxNGxTNXVhbTZsaXZLTmliNWto?= =?utf-8?B?U1I3anEydmh1VVBCcnRGT2xVb0JRQktCUmkrQVZzL0s3TnZERWgrSm9XcXZk?= =?utf-8?B?ZU8vc25rV2ZLTmltK0dlYy9iUENQRzAvNXUyRkFaQUpna1JxQVdSRkVtYWlo?= =?utf-8?B?NUdHRFhhM3BTOGhUK0k0U3VVMDlydEdjQjF6SWU1cjZxVDNkNEo4SVA3OEd3?= =?utf-8?B?Q1paejFvMk5PZFlmTGpXeVVhd3VEZ1pHcmdPVGR4THB6d1hrcWptdnQvTmNW?= =?utf-8?B?SlNGVkZ5OXNNbjZnU1VwRHZLaXplaW1EbG1DUUtWL3VrSG5FVm45cjVRS2or?= =?utf-8?B?N1pYNXRSQjFVTDJHZmxwMUwzUXh6dzJSQktwVEhIbGliU0YvVHk2M3ZubE9J?= =?utf-8?B?Sk9jeUZYaFFFcy8wRzZnMzAzR2VUbmtCYmtMTEpDWkpWcklBeDNjNStUSWVw?= =?utf-8?B?UUdOREszWTN6M0J1OEt5Zys2YWlneWxjQmdtWWVvck9OSmtEbFdkOUx1SXZu?= =?utf-8?B?cjhiajZicEJzTFlzUWpNN1duME1xTVFyaXdLWXlVaXZOc0tVc3ZlblFTZ0lx?= =?utf-8?B?aG9DSS9udWhIV3VKejM3NW9nVHRpOUNpdDAzR0VBa0grYTdlRVRVZDlwTEFa?= =?utf-8?B?RTVFZWxzOW1mREhEdU5ERWpTY1hsMWo4ZDZFTkk4RnE4ekFQRUE1UHQ5bXZV?= =?utf-8?B?REFTWDJqVk5KaDVBTXZ4UWtMMUtXcE1oVlBsWVNEbzRzUXhyV3IxN0h3WjZJ?= =?utf-8?B?SlFka0pvMFZnZFc3WEE2ZEdGaTBhbEJXeFJSMStHbGUyVVlCV1gzN01OQlk3?= =?utf-8?B?WE1jZkRlRkN0Q3c3VVdPWmVROTRkb0EvRnZ2K1VJS3dZc25ObU9NYThFR3RS?= =?utf-8?B?N1N2cmpaSUxjNzNETEpqU1A4ODNWOUx2NDlMMldudFdMSlJGNnBjcnYveE5T?= =?utf-8?B?L1lvUlRDMkpCLzArRmxyYlZDVFdNbXFsdWdRc1ViSnlsTFpCemkvSEl0NytB?= =?utf-8?B?b0lZdGQ2aDFhMEJSeHZud2lFK0NSSzRvQmpsaWRNYk1QTU5GcWNaNThHRjcy?= =?utf-8?Q?nXQcLfYwIll14I1bjHF6MsN7aWLEAyCLnhloABN?= X-MS-Exchange-CrossTenant-Network-Message-Id: bddc1ab4-f72e-4a7c-ca9b-08d92fde675f X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Jun 2021 09:17:31.5250 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: aysi2Bpr7TpRaLtXJS89E+ygQmpzN3iAttsvaHIwDrZNLQtojYQPuoN6Rt06FKh+N2czAG//3zYe6d/pQjDGqWcKnAsSDhfwRYT7RDwEIvM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR03MB4999 X-OriginatorOrg: citrix.com On 15/06/2021 09:12, Roger Pau Monné wrote: > On Mon, Jun 14, 2021 at 06:01:17PM +0200, Jan Beulich wrote: >> On 14.06.2021 15:27, Roger Pau Monné wrote: >>> On Mon, Jun 14, 2021 at 01:53:09PM +0200, Jan Beulich wrote: >>>> On 14.06.2021 13:15, Igor Druzhinin wrote: >>>>> Hi, Boris, Stephen, Roger, >>>>> >>>>> We have stress tested recent changes on staging-4.13 which includes a >>>>> backport of the subject. Since the backport is identical to the >>>>> master branch and all of the pre-reqs are in place - we have no reason >>>>> to believe the issue is not the same on master. >>>>> >>>>> Here is what we got by running heavy stress testing including multiple >>>>> repeated VM lifecycle operations with storage and network load: >>>>> >>>>> >>>>> Assertion 'timer->status >= TIMER_STATUS_inactive' failed at timer.c:287 >>>>> ----[ Xen-4.13.3-10.7-d x86_64 debug=y Not tainted ]---- >>>>> CPU: 17 >>>>> RIP: e008:[] common/timer.c#active_timer+0xc/0x1b >>>>> RFLAGS: 0000000000010046 CONTEXT: hypervisor (d675v0) >>>>> rax: 0000000000000000 rbx: ffff83137a8ed300 rcx: 0000000000000000 >>>>> rdx: ffff83303fff7fff rsi: ffff83303fff2549 rdi: ffff83137a8ed300 >>>>> rbp: ffff83303fff7cf8 rsp: ffff83303fff7cf8 r8: 0000000000000001 >>>>> r9: 0000000000000000 r10: 0000000000000011 r11: 0000168b0cc08083 >>>>> r12: 0000000000000000 r13: ffff82d0805cf300 r14: ffff82d0805cf300 >>>>> r15: 0000000000000292 cr0: 0000000080050033 cr4: 00000000000426e0 >>>>> cr3: 00000013c1a32000 cr2: 0000000000000000 >>>>> fsb: 0000000000000000 gsb: 0000000000000000 gss: 0000000000000000 >>>>> ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: 0000 cs: e008 >>>>> Xen code around (common/timer.c#active_timer+0xc/0x1b): >>>>> 0f b6 47 2a 84 c0 75 02 <0f> 0b 3c 04 76 02 0f 0b 3c 02 0f 97 c0 5d c3 55 >>>>> Xen stack trace from rsp=ffff83303fff7cf8: >>>>> ffff83303fff7d48 ffff82d0802479f1 0000168b0192b846 ffff83137a8ed328 >>>>> 000000001d0776eb ffff83137a8ed2c0 ffff83133ee47568 ffff83133ee47000 >>>>> ffff83133ee47560 ffff832b1a0cd000 ffff83303fff7d78 ffff82d08031e74e >>>>> ffff83102d898000 ffff83133ee47000 ffff83102db8d000 0000000000000011 >>>>> ffff83303fff7dc8 ffff82d08027df19 0000000000000000 ffff83133ee47060 >>>>> ffff82d0805d0088 ffff83102d898000 ffff83133ee47000 0000000000000011 >>>>> 0000000000000001 0000000000000011 ffff83303fff7e08 ffff82d0802414e0 >>>>> ffff83303fff7df8 0000168b0192b846 ffff83102d8a4660 0000168b0192b846 >>>>> ffff83102d8a4720 0000000000000011 ffff83303fff7ea8 ffff82d080241d6c >>>>> ffff83133ee47000 ffff831244137a50 ffff83303fff7e48 ffff82d08031b5b8 >>>>> ffff83133ee47000 ffff832b1a0cd000 ffff83303fff7e68 ffff82d080312b65 >>>>> ffff83133ee47000 0000000000000000 ffff83303fff7ee8 ffff83102d8a4678 >>>>> ffff83303fff7ee8 ffff82d0805d6380 ffff82d0805d5b00 ffffffffffffffff >>>>> ffff83303fff7fff 0000000000000000 ffff83303fff7ed8 ffff82d0802431f5 >>>>> ffff83133ee47000 0000000000000000 0000000000000000 0000000000000000 >>>>> ffff83303fff7ee8 ffff82d08024324a 00007ccfc00080e7 ffff82d08033930b >>>>> ffffffffb0ebd5a0 000000000000000d 0000000000000062 0000000000000097 >>>>> 000000000000001e 000000000000001f ffffffffb0ebd5ad 0000000000000000 >>>>> 0000000000000005 000000000003d91d 0000000000000000 0000000000000000 >>>>> 00000000000003d5 000000000000001e 0000000000000000 0000beef0000beef >>>>> Xen call trace: >>>>> [] R common/timer.c#active_timer+0xc/0x1b >>>>> [] F stop_timer+0xf5/0x188 >>>>> [] F pt_save_timer+0x45/0x8a >>>>> [] F context_switch+0xf9/0xee0 >>>>> [] F common/schedule.c#sched_context_switch+0x146/0x151 >>>>> [] F common/schedule.c#schedule+0x28a/0x299 >>>>> [] F common/softirq.c#__do_softirq+0x85/0x90 >>>>> [] F do_softirq+0x13/0x15 >>>>> [] F vmx_asm_do_vmentry+0x2b/0x30 >>>>> >>>>> **************************************** >>>>> Panic on CPU 17: >>>>> Assertion 'timer->status >= TIMER_STATUS_inactive' failed at timer.c:287 >>>>> **************************************** >>>> Since this suggests a timer was found on the list without ever having been >>>> initialized, I've spotted a case where this indeed could now happen. Could >>>> you give the patch below a try? >>>> >>>> Jan >>>> >>>> x86/vpt: fully init timers before putting onto list >>>> >>>> With pt_vcpu_lock() no longer acquiring the pt_migrate lock, parties >>>> iterating the list and acting on the timers of the list entries will no >>>> longer be kept from entering their loops by create_periodic_time()'s >>>> holding of that lock. Therefore at least init_timer() needs calling >>>> ahead of list insertion, but keep this and set_timer() together. >>>> >>>> Fixes: 8113b02f0bf8 ("x86/vpt: do not take pt_migrate rwlock in some cases") >>>> Reported-by: Igor Druzhinin >>>> Signed-off-by: Jan Beulich >>> Thanks for looking into this so quickly, and sorry for not realizing >>> myself when relaxing the locking. Adding the timer to the list without >>> it being fully initialized was a latent issue even if protected by the >>> lock initially. >>> >>> Provided testing shows the issue is fixed: >> I guess the change here is needed anyway, even if testing finds there's >> still something amiss? > Indeed, just wondered whether there might be other instances using a > similar pattern, but I'm not able to spot any. > > It might even be better to fix other issues (if any) on a different > commit. To be honest, this change is clearly good, and necessary.  I'd be tempted to commit it now, as is, irrespective of whether there are further bugs in this area. ~Andrew