[PATCH 1/7] drm/amdgpu: Avoid reclaim fs while eviction lock

[Alex Sierra]

[Why]
Avoid reclaim filesystem while eviction lock is held called from
MMU notifier.

[How]
Setting PF_MEMALLOC_NOFS flags while eviction mutex is locked.
Using memalloc_nofs_save / memalloc_nofs_restore API.

Change-Id: I5531c9337836e7d4a430df3f16dcc82888e8018c
Signed-off-by: Alex Sierra <alex.sierra at amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 40 +++++++++++++++++++++-----
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h |  6 +++-
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index b999b67ff57a..d6aba4f9df74 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -82,6 +82,32 @@ struct amdgpu_prt_cb {
 	struct dma_fence_cb cb;
 };
 
+/**
+ * vm eviction_lock can be taken in MMU notifiers. Make sure no reclaim-FS
+ * happens while holding this lock anywhere to prevent deadlocks when
+ * an MMU notifier runs in reclaim-FS context.
+ */
+static inline void amdgpu_vm_eviction_lock(struct amdgpu_vm *vm)
+{
+	mutex_lock(&vm->eviction_lock);
+	vm->saved_flags = memalloc_nofs_save();
+}
+
+static inline int amdgpu_vm_eviction_trylock(struct amdgpu_vm *vm)
+{
+	if (mutex_trylock(&vm->eviction_lock)) {
+		vm->saved_flags = memalloc_nofs_save();
+		return 1;
+	}
+	return 0;
+}
+
+static inline void amdgpu_vm_eviction_unlock(struct amdgpu_vm *vm)
+{
+	memalloc_nofs_restore(vm->saved_flags);
+	mutex_unlock(&vm->eviction_lock);
+}
+
 /**
  * amdgpu_vm_level_shift - return the addr shift for each level
  *
@@ -678,9 +704,9 @@ int amdgpu_vm_validate_pt_bos(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 		}
 	}
 
-	mutex_lock(&vm->eviction_lock);
+	amdgpu_vm_eviction_lock(vm);
 	vm->evicting = false;
-	mutex_unlock(&vm->eviction_lock);
+	amdgpu_vm_eviction_unlock(vm);
 
 	return 0;
 }
@@ -1559,7 +1585,7 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
 	if (!(flags & AMDGPU_PTE_VALID))
 		owner = AMDGPU_FENCE_OWNER_KFD;
 
-	mutex_lock(&vm->eviction_lock);
+	amdgpu_vm_eviction_lock(vm);
 	if (vm->evicting) {
 		r = -EBUSY;
 		goto error_unlock;
@@ -1576,7 +1602,7 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
 	r = vm->update_funcs->commit(&params, fence);
 
 error_unlock:
-	mutex_unlock(&vm->eviction_lock);
+	amdgpu_vm_eviction_unlock(vm);
 	return r;
 }
 
@@ -2537,18 +2563,18 @@ bool amdgpu_vm_evictable(struct amdgpu_bo *bo)
 		return false;
 
 	/* Try to block ongoing updates */
-	if (!mutex_trylock(&bo_base->vm->eviction_lock))
+	if (!amdgpu_vm_eviction_trylock(bo_base->vm))
 		return false;
 
 	/* Don't evict VM page tables while they are updated */
 	if (!dma_fence_is_signaled(bo_base->vm->last_direct) ||
 	    !dma_fence_is_signaled(bo_base->vm->last_delayed)) {
-		mutex_unlock(&bo_base->vm->eviction_lock);
+		amdgpu_vm_eviction_unlock(bo_base->vm);
 		return false;
 	}
 
 	bo_base->vm->evicting = true;
-	mutex_unlock(&bo_base->vm->eviction_lock);
+	amdgpu_vm_eviction_unlock(bo_base->vm);
 	return true;
 }
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index 100547f094ff..c21a36bebc0c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -30,6 +30,7 @@
 #include <drm/gpu_scheduler.h>
 #include <drm/drm_file.h>
 #include <drm/ttm/ttm_bo_driver.h>
+#include <linux/sched/mm.h>
 
 #include "amdgpu_sync.h"
 #include "amdgpu_ring.h"
@@ -242,9 +243,12 @@ struct amdgpu_vm {
 	/* tree of virtual addresses mapped */
 	struct rb_root_cached	va;
 
-	/* Lock to prevent eviction while we are updating page tables */
+	/* Lock to prevent eviction while we are updating page tables
+	 * use vm_eviction_lock/unlock(vm)
+	 */
 	struct mutex		eviction_lock;
 	bool			evicting;
+	unsigned int		saved_flags;
 
 	/* BOs who needs a validation */
 	struct list_head	evicted;
-- 
2.17.1