Re: [PATCH v5 1/1] drm/amdgpu: Fix amdgpu_vm_pt_free warning

[Christian König <christian.koenig@xxxxxxx>]

Am 14.09.22 um 19:45 schrieb Felix Kuehling:
> Am 2022-09-14 um 12:08 schrieb Philip Yang:
> > Free page table BO from vm resv unlocked context generate below
> > warnings.
> >
> > Add a pt_free_work in vm to free page table BO from vm->pt_freed list.
> > pass vm resv unlock status from page table update caller, and add vm_bo
> > entry to vm->pt_freed list and schedule the pt_free_work if calling with
> > vm resv unlocked.
> >
> > WARNING: CPU: 12 PID: 3238 at
> > drivers/gpu/drm/ttm/ttm_bo.c:106 ttm_bo_set_bulk_move+0xa1/0xc0
> > Call Trace:
> >   amdgpu_vm_pt_free+0x42/0xd0 [amdgpu]
> >   amdgpu_vm_pt_free_dfs+0xb3/0xf0 [amdgpu]
> >   amdgpu_vm_ptes_update+0x52d/0x850 [amdgpu]
> >   amdgpu_vm_update_range+0x2a6/0x640 [amdgpu]
> >   svm_range_unmap_from_gpus+0x110/0x300 [amdgpu]
> >   svm_range_cpu_invalidate_pagetables+0x535/0x600 [amdgpu]
> >   __mmu_notifier_invalidate_range_start+0x1cd/0x230
> >   unmap_vmas+0x9d/0x140
> >   unmap_region+0xa8/0x110
> >
> > Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  5 +++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h    |  6 ++++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 41 +++++++++++++++++++++--
> >   3 files changed, 49 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > index 59cac347baa3..20cfc8c9635b 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > @@ -2022,6 +2022,9 @@ int amdgpu_vm_init(struct amdgpu_device *adev, 
> > struct amdgpu_vm *vm)
> >       spin_lock_init(&vm->invalidated_lock);
> >       INIT_LIST_HEAD(&vm->freed);
> >       INIT_LIST_HEAD(&vm->done);
> > +    INIT_LIST_HEAD(&vm->pt_freed);
> > +    INIT_WORK(&vm->pt_free_work, amdgpu_vm_pt_free_work);
> > +    spin_lock_init(&vm->pt_free_lock);
> >         /* create scheduler entities for page table updates */
> >       r = drm_sched_entity_init(&vm->immediate, 
> > DRM_SCHED_PRIORITY_NORMAL,
> > @@ -2223,6 +2226,8 @@ void amdgpu_vm_fini(struct amdgpu_device *adev, 
> > struct amdgpu_vm *vm)
> >         amdgpu_amdkfd_gpuvm_destroy_cb(adev, vm);
> >   +    flush_work(&vm->pt_free_work);
> > +
> >       root = amdgpu_bo_ref(vm->root.bo);
> >       amdgpu_bo_reserve(root, true);
> >       amdgpu_vm_set_pasid(adev, vm, 0);
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > index 9ecb7f663e19..b77fe838c327 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> > @@ -276,6 +276,11 @@ struct amdgpu_vm {
> >       /* BOs which are invalidated, has been updated in the PTs */
> >       struct list_head        done;
> >   +    /* PT BOs scheduled to free and fill with zero if vm_resv is 
> > not hold */
> > +    struct list_head    pt_freed;
> > +    struct work_struct    pt_free_work;
> > +    spinlock_t        pt_free_lock;
> > +
> >       /* contains the page directory */
> >       struct amdgpu_vm_bo_base     root;
> >       struct dma_fence    *last_update;
> > @@ -471,6 +476,7 @@ int amdgpu_vm_pde_update(struct 
> > amdgpu_vm_update_params *params,
> >   int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
> >                 uint64_t start, uint64_t end,
> >                 uint64_t dst, uint64_t flags);
> > +void amdgpu_vm_pt_free_work(struct work_struct *work);
> >     #if defined(CONFIG_DEBUG_FS)
> >   void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct 
> > seq_file *m);
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> > index 88de9f0d4728..c16579471f22 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
> > @@ -641,6 +641,27 @@ static void amdgpu_vm_pt_free(struct 
> > amdgpu_vm_bo_base *entry)
> >       amdgpu_bo_unref(&entry->bo);
> >   }
> >   +void amdgpu_vm_pt_free_work(struct work_struct *work)
> > +{
> > +    struct amdgpu_vm_bo_base *entry, *next;
> > +    struct amdgpu_vm *vm;
> > +    LIST_HEAD(pt_freed);
> > +
> > +    vm = container_of(work, struct amdgpu_vm, pt_free_work);
> > +
> > +    spin_lock(&vm->pt_free_lock);
> > +    list_splice_init(&vm->pt_freed, &pt_freed);
> > +    spin_unlock(&vm->pt_free_lock);
> > +
> > +    // flush_work in amdgpu_vm_fini ensure vm->root.bo is valid
> > +    amdgpu_bo_reserve(vm->root.bo, true);
> > +
> > +    list_for_each_entry_safe(entry, next, &pt_freed, vm_status)
> > +        amdgpu_vm_pt_free(entry);
> > +
> > +    amdgpu_bo_unreserve(vm->root.bo);
> > +}
> > +
> >   /**
> >    * amdgpu_vm_pt_free_dfs - free PD/PT levels
> >    *
> > @@ -652,11 +673,24 @@ static void amdgpu_vm_pt_free(struct 
> > amdgpu_vm_bo_base *entry)
> >    */
> >   static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
> >                     struct amdgpu_vm *vm,
> > -                  struct amdgpu_vm_pt_cursor *start)
> > +                  struct amdgpu_vm_pt_cursor *start,
> > +                  bool unlocked)
> >   {
> >       struct amdgpu_vm_pt_cursor cursor;
> >       struct amdgpu_vm_bo_base *entry;
> >   +    if (unlocked) {
> > +        spin_lock(&vm->pt_free_lock);
> > +        for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
> > +            list_move(&entry->vm_status, &vm->pt_freed);
> > +
> > +        if (start)
> > +            list_move(&start->entry->vm_status, &vm->pt_freed);
> > +        spin_unlock(&vm->pt_free_lock);
>
> Question for Christian: list_move will take the entry off another 
> vm_status list (evicted, idle, invalidated, relocated). I don't think 
> this is safe without holding a reservation lock in most cases. Since 
> the point here is to maintain a list of PTs to be freed without 
> locking a reservation, is the vm_status really the right way to do this?

Oh, good point. This means we need to protect the whole state machine 
with a spinlock or use a separate deleted list.

I don't see how we can easily use a separate list here, but we already 
have the invalidated_lock, maybe we need to rename this one to status 
lock and use it for all cases.

Regards,
Christian.

> Regards,
>   Felix
>
>
> > + schedule_work(&vm->pt_free_work);
> > +        return;
> > +    }
> > +
> >       for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
> >           amdgpu_vm_pt_free(entry);
> >   @@ -673,7 +707,7 @@ static void amdgpu_vm_pt_free_dfs(struct 
> > amdgpu_device *adev,
> >    */
> >   void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct 
> > amdgpu_vm *vm)
> >   {
> > -    amdgpu_vm_pt_free_dfs(adev, vm, NULL);
> > +    amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
> >   }
> >     /**
> > @@ -966,7 +1000,8 @@ int amdgpu_vm_ptes_update(struct 
> > amdgpu_vm_update_params *params,
> >                   if (cursor.entry->bo) {
> >                       params->table_freed = true;
> >                       amdgpu_vm_pt_free_dfs(adev, params->vm,
> > -                                  &cursor);
> > +                                  &cursor,
> > +                                  params->unlocked);
> >                   }
> >                   amdgpu_vm_pt_next(adev, &cursor);
> >               }