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

[Philip Yang <yangp@xxxxxxx>]

On 2022-09-15 02:21, Christian König wrote:
> 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.

Rename invalidate_lock to status_lock, then we can use it for 
vm->pt_freed list, don't need another vm->pt_free_lock, this is good.

invalidate_lock is used to protect list vm->invalidate and vm->done 
right now, other vm list evicted/relocated/moved/idle/freed are 
protected by reservation lock. Do we need protect all vm lists 
operations with status_lock as well to ensure it is safe to take entry 
from vm_status lists for unlocked context?

Regards,

Philip

> 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);
> > >               }