Re: [PATCH 1/5] drm/amdgpu: Avoid reclaim fs while eviction lock

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Am 20.12.19 um 07:24 schrieb 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@xxxxxxx>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 14 ++++++-------
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 28 +++++++++++++++++++++++++-
  2 files changed, 34 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..b36daa6230fb 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -678,9 +678,9 @@ int amdgpu_vm_validate_pt_bos(struct amdgpu_device *adev, struct amdgpu_vm *vm,
  		}
  	}
- mutex_lock(&vm->eviction_lock);
+	vm_eviction_lock(vm);
  	vm->evicting = false;
-	mutex_unlock(&vm->eviction_lock);
+	vm_eviction_unlock(vm);
return 0;
  }
@@ -1559,7 +1559,7 @@ 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);
+	vm_eviction_lock(vm);
  	if (vm->evicting) {
  		r = -EBUSY;
  		goto error_unlock;
@@ -1576,7 +1576,7 @@ 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);
+	vm_eviction_unlock(vm);
  	return r;
  }
@@ -2537,18 +2537,18 @@ bool amdgpu_vm_evictable(struct amdgpu_bo *bo)
  		return false;
/* Try to block ongoing updates */
-	if (!mutex_trylock(&bo_base->vm->eviction_lock))
+	if (!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);
+		vm_eviction_unlock(bo_base->vm);
  		return false;
  	}
bo_base->vm->evicting = true;
-	mutex_unlock(&bo_base->vm->eviction_lock);
+	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..d35aa76469ec 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;
@@ -436,4 +440,26 @@ void amdgpu_vm_move_to_lru_tail(struct amdgpu_device *adev,
  				struct amdgpu_vm *vm);
  void amdgpu_vm_del_from_lru_notify(struct ttm_buffer_object *bo);
+/* 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 vm_eviction_lock(struct amdgpu_vm *vm)

Please add a proper amdgpu_ prefix to the function names.

Additional to that please don't put local static functions into the header, those shouldn't be used outside of the VM code.

Christian.

+{
+	mutex_lock(&vm->eviction_lock);
+	vm->saved_flags = memalloc_nofs_save();
+}
+static inline int 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 vm_eviction_unlock(struct amdgpu_vm *vm)
+{
+	memalloc_nofs_restore(vm->saved_flags);
+	mutex_unlock(&vm->eviction_lock);
+}
  #endif

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