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Fri, 18 Oct 2024 14:40:43 +0000 Message-ID: <52c18f08-0d8a-4419-ab36-9f072c54f9cf@intel.com> Date: Fri, 18 Oct 2024 16:40:37 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] drm/xe/ufence: Signal ufence immediately when possible To: Matthew Auld , References: <20241018124710.1536948-1-nirmoy.das@intel.com> <2ef62119-1b98-4e5f-8218-0c99b4dbce36@intel.com> Content-Language: en-US From: Nirmoy Das In-Reply-To: <2ef62119-1b98-4e5f-8218-0c99b4dbce36@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: TLZP290CA0010.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:9::9) To DS0PR11MB6541.namprd11.prod.outlook.com (2603:10b6:8:d3::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB6541:EE_|PH0PR11MB4903:EE_ X-MS-Office365-Filtering-Correlation-Id: 57c22af4-11f2-4278-fd47-08dcef82d7df X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; 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>>   } >>   -static void user_fence_worker(struct work_struct *w) >> +static void signal_user_fence(struct xe_user_fence *ufence) >>   { >> -    struct xe_user_fence *ufence = container_of(w, struct xe_user_fence, worker); >> - >>       if (mmget_not_zero(ufence->mm)) { >>           kthread_use_mm(ufence->mm); >>           if (copy_to_user(ufence->addr, &ufence->value, sizeof(ufence->value))) > > This can end up in a CPU fault handler? There might be some locking issues if caller is say holding dma-resv. For example the caller in xe_exec which is holding dma-resv. If it can indeed hit this path, then we might get some splats/deadlocks, I think. What is the connection between writting into ufence addr  and dma-resv  ? Trying to understand this locking problem. it looks like I have to use a worker anyway to do kthread_use_mm(), https://intel-gfx-ci.01.org/tree/intel-xe/xe-pw-140169v1/bat-atsm-2/igt@xe_exec_balancer@no-exec-cm-virtual-basic.html Regards, Nirmoy > >> @@ -89,6 +87,14 @@ static void user_fence_worker(struct work_struct *w) >>       user_fence_put(ufence); >>   } >>   +static void user_fence_worker(struct work_struct *w) >> +{ >> +    struct xe_user_fence *ufence = container_of(w, struct xe_user_fence, >> +                            worker); >> + >> +    signal_user_fence(ufence); >> +} >> + >>   static void kick_ufence(struct xe_user_fence *ufence, struct dma_fence *fence) >>   { >>       INIT_WORK(&ufence->worker, user_fence_worker); >> @@ -236,7 +242,8 @@ void xe_sync_entry_signal(struct xe_sync_entry *sync, struct dma_fence *fence) >>           err = dma_fence_add_callback(fence, &sync->ufence->cb, >>                            user_fence_cb); >>           if (err == -ENOENT) { >> -            kick_ufence(sync->ufence, fence); >> +            /* signal the ufence immediately if fence is already signalled */ >> +            signal_user_fence(sync->ufence); >>           } else if (err) { >>               XE_WARN_ON("failed to add user fence"); >>               user_fence_put(sync->ufence);