[PATCH] drm/amdgpu: fix a potential circular locking dependency

[Dennis Li]

[  653.902305] ======================================================
[  653.902928] WARNING: possible circular locking dependency detected
[  653.903517] 5.6.0-deli-v5.6-2848-g3f3109b0e75f #1 Tainted: G           OE
[  653.904098] ------------------------------------------------------
[  653.904675] amdgpu_test/3975 is trying to acquire lock:
[  653.905241] ffff97848f8647a0 (&adev->reset_sem){.+.+}, at: amdgpu_gem_va_ioctl+0x286/0x4f0 [amdgpu]
[  653.905953]
               but task is already holding lock:
[  653.907087] ffff9744adbee1f8 (reservation_ww_class_mutex){+.+.}, at: ttm_eu_reserve_buffers+0x1ae/0x520 [ttm]
[  653.907694]
               which lock already depends on the new lock.

[  653.909423]
               the existing dependency chain (in reverse order) is:
[  653.910594]
               -> #1 (reservation_ww_class_mutex){+.+.}:
[  653.911759]        __ww_mutex_lock.constprop.15+0xca/0x1120
[  653.912350]        ww_mutex_lock+0x73/0x80
[  653.913044]        amdgpu_amdkfd_alloc_gtt_mem+0xde/0x380 [amdgpu]
[  653.913724]        kgd2kfd_device_init+0x13f/0x5e0 [amdgpu]
[  653.914388]        amdgpu_amdkfd_device_init+0x155/0x190 [amdgpu]
[  653.915033]        amdgpu_device_init+0x1303/0x1e10 [amdgpu]
[  653.915685]        amdgpu_driver_load_kms+0x5c/0x2c0 [amdgpu]
[  653.916349]        amdgpu_pci_probe+0x11d/0x200 [amdgpu]
[  653.916959]        local_pci_probe+0x47/0xa0
[  653.917570]        work_for_cpu_fn+0x1a/0x30
[  653.918184]        process_one_work+0x29e/0x630
[  653.918803]        worker_thread+0x22b/0x3f0
[  653.919427]        kthread+0x12f/0x150
[  653.920047]        ret_from_fork+0x3a/0x50
[  653.920661]
               -> #0 (&adev->reset_sem){.+.+}:
[  653.921893]        __lock_acquire+0x13ec/0x16e0
[  653.922531]        lock_acquire+0xb8/0x1c0
[  653.923174]        down_read+0x48/0x230
[  653.923886]        amdgpu_gem_va_ioctl+0x286/0x4f0 [amdgpu]
[  653.924588]        drm_ioctl_kernel+0xb6/0x100 [drm]
[  653.925283]        drm_ioctl+0x389/0x450 [drm]
[  653.926013]        amdgpu_drm_ioctl+0x4f/0x80 [amdgpu]
[  653.926686]        ksys_ioctl+0x98/0xb0
[  653.927357]        __x64_sys_ioctl+0x1a/0x20
[  653.928030]        do_syscall_64+0x5f/0x250
[  653.928697]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  653.929373]
               other info that might help us debug this:

[  653.931356]  Possible unsafe locking scenario:

[  653.932647]        CPU0                    CPU1
[  653.933287]        ----                    ----
[  653.933911]   lock(reservation_ww_class_mutex);
[  653.934530]                                lock(&adev->reset_sem);
[  653.935154]                                lock(reservation_ww_class_mutex);
[  653.935766]   lock(&adev->reset_sem);
[  653.936360]
                *** DEADLOCK ***

[  653.938028] 2 locks held by amdgpu_test/3975:
[  653.938574]  #0: ffffb2a862d6bcd0 (reservation_ww_class_acquire){+.+.}, at: amdgpu_gem_va_ioctl+0x39b/0x4f0 [amdgpu]
[  653.939233]  #1: ffff9744adbee1f8 (reservation_ww_class_mutex){+.+.}, at: ttm_eu_reserve_buffers+0x1ae/0x520 [ttm]

change the order of reservation_ww_class_mutex and adev->reset_sem in
amdgpu_gem_va_ioctl the same as ones in amdgpu_amdkfd_alloc_gtt_mem, to
avoid potential dead lock.

Signed-off-by: Dennis Li <Dennis.Li at amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index ee1e8fff83b2..fc889c477696 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -652,6 +652,8 @@ int amdgpu_gem_va_ioctl(struct drm_device *dev, void *data,
 		abo = NULL;
 	}
 
+	down_read(&adev->reset_sem);
+
 	amdgpu_vm_get_pd_bo(&fpriv->vm, &list, &vm_pd);
 
 	r = ttm_eu_reserve_buffers(&ticket, &list, true, &duplicates);
@@ -670,8 +672,6 @@ int amdgpu_gem_va_ioctl(struct drm_device *dev, void *data,
 		bo_va = NULL;
 	}
 
-	down_read(&adev->reset_sem);
-
 	switch (args->operation) {
 	case AMDGPU_VA_OP_MAP:
 		va_flags = amdgpu_gem_va_map_flags(adev, args->flags);
@@ -701,12 +701,11 @@ int amdgpu_gem_va_ioctl(struct drm_device *dev, void *data,
 		amdgpu_gem_va_update_vm(adev, &fpriv->vm, bo_va,
 					args->operation);
 
-	up_read(&adev->reset_sem);
-
 error_backoff:
 	ttm_eu_backoff_reservation(&ticket, &list);
 
 error_unref:
+	up_read(&adev->reset_sem);
 	drm_gem_object_put_unlocked(gobj);
 	return r;
 }
-- 
2.17.1