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mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from DS0PR11MB6541.namprd11.prod.outlook.com (2603:10b6:8:d3::14) by SA0PR11MB4655.namprd11.prod.outlook.com (2603:10b6:806:9d::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8069.23; Fri, 18 Oct 2024 15:29:14 +0000 Received: from DS0PR11MB6541.namprd11.prod.outlook.com ([fe80::e268:87f2:3bd1:1347]) by DS0PR11MB6541.namprd11.prod.outlook.com ([fe80::e268:87f2:3bd1:1347%5]) with mapi id 15.20.8069.020; Fri, 18 Oct 2024 15:29:14 +0000 Message-ID: Date: Fri, 18 Oct 2024 17:29:09 +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> <52c18f08-0d8a-4419-ab36-9f072c54f9cf@intel.com> <9fb1e3a2-c4ab-4520-996f-b5d20f634093@intel.com> Content-Language: en-US From: Nirmoy Das In-Reply-To: <9fb1e3a2-c4ab-4520-996f-b5d20f634093@intel.com> Content-Type: text/plain; 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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. > > Basically the user can have the ufence be an mmap address from a BO, so it can basically hit xe_gem_fault() here. The mmap lock should already be tainted with dma-resv, so might_fault() should complain. I see what you mean, haven't thought about it. > >> >> >> 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 > > Yes, exactly that just with might_fault() in copy_to_user. Good to see that CI caught this. From the logs we can also see the exact dma-resv splat as per above: Back to the previous rev but with the bool as suggested by Matt B. Thanks, Nirmoy > > 4> [233.110447] xe_exec_balance/3613 is trying to acquire lock: > <4> [233.110457] ff11000100085998 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x43/0x90 > <4> [233.110481] > but task is already holding lock: > <4> [233.110491] ff110001231a1da0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_exec_lock_obj+0x88/0x2b0 [drm_exec] > <4> [233.110517] > which lock already depends on the new lock. > <4> [233.110530] > the existing dependency chain (in reverse order) is: > <4> [233.110540] > -> #2 (reservation_ww_class_mutex){+.+.}-{3:3}: > <4> [233.110558]        __ww_mutex_lock.constprop.0+0xe1/0x14d0 > <4> [233.110574]        ww_mutex_lock+0x3c/0xa0 > <4> [233.110586]        dma_resv_lockdep+0x1a4/0x340 > <4> [233.110599]        do_one_initcall+0x76/0x3e0 > <4> [233.110615]        kernel_init_freeable+0x3dc/0x690 > <4> [233.110632]        kernel_init+0x1b/0x200 > <4> [233.110645]        ret_from_fork+0x3a/0x60 > <4> [233.110658]        ret_from_fork_asm+0x1a/0x30 > <4> [233.110671] > -> #1 (reservation_ww_class_acquire){+.+.}-{0:0}: > <4> [233.110689]        dma_resv_lockdep+0x180/0x340 > <4> [233.110699]        do_one_initcall+0x76/0x3e0 > <4> [233.110713]        kernel_init_freeable+0x3dc/0x690 > <4> [233.110728]        kernel_init+0x1b/0x200 > <4> [233.110740]        ret_from_fork+0x3a/0x60 > <4> [233.110752]        ret_from_fork_asm+0x1a/0x30 > <4> [233.110764] > -> #0 (&mm->mmap_lock){++++}-{3:3}: > <4> [233.110780]        __lock_acquire+0x1623/0x2800 > <4> [233.110794]        lock_acquire+0xc5/0x2f0 > <4> [233.110807]        __might_fault+0x63/0x90 > <4> [233.110818]        _copy_to_user+0x23/0x70 > <4> [233.110830]        signal_user_fence+0x46/0xd0 [xe] > <4> [233.111108]        xe_sync_entry_signal+0x14e/0x1b0 [xe] > <4> [233.111366]        vm_bind_ioctl_ops_execute+0x3f8/0x910 [xe] > <4> [233.111665]        xe_vm_bind_ioctl+0x1623/0x22a0 [xe] > <4> [233.111951]        drm_ioctl_kernel+0xb1/0x120 [drm] > <4> [233.112052]        drm_ioctl+0x2e8/0x5a0 [drm] > <4> [233.112140]        xe_drm_ioctl+0x53/0x80 [xe] > <4> [233.112331]        __x64_sys_ioctl+0x95/0xd0 > <4> [233.112342]        x64_sys_call+0x1089/0x2060 > <4> [233.112355]        do_syscall_64+0x87/0x140 > <4> [233.112365]        entry_SYSCALL_64_after_hwframe+0x76/0x7e > <4> [233.112380] > >> >> >> 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);