Re: [PATCH 25/39] drm/i915: Pull VM lists under the VM mutex.

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Quoting Tvrtko Ursulin (2019-01-02 13:21:17)
> 
> On 02/01/2019 09:41, Chris Wilson wrote:
> 
> Give it a bit of commit text please.

    A starting point to counter the pervasive struct_mutex. For the goal of
    avoiding (or at least blocking under them!) global locks during user
    request submission, a simple but important step is being able to manage
    each clients GTT separately. For which, we want to replace using the
    struct_mutex as the guard for all things GTT/VM and switch instead to a
    specific mutex inside i915_address_space.

> 
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/i915_gem.c                 | 14 ++++++++------
> >   drivers/gpu/drm/i915/i915_gem_evict.c           |  2 ++
> >   drivers/gpu/drm/i915/i915_gem_gtt.c             | 15 +++++++++++++--
> >   drivers/gpu/drm/i915/i915_gem_shrinker.c        |  4 ++++
> >   drivers/gpu/drm/i915/i915_gem_stolen.c          |  2 ++
> >   drivers/gpu/drm/i915/i915_vma.c                 | 11 +++++++++++
> >   drivers/gpu/drm/i915/selftests/i915_gem_evict.c |  3 +++
> >   drivers/gpu/drm/i915/selftests/i915_gem_gtt.c   |  3 +++
> >   8 files changed, 46 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index d9e1dcee176c..66445e34c93c 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -246,18 +246,19 @@ int
> >   i915_gem_get_aperture_ioctl(struct drm_device *dev, void *data,
> >                           struct drm_file *file)
> >   {
> > -     struct drm_i915_private *dev_priv = to_i915(dev);
> > -     struct i915_ggtt *ggtt = &dev_priv->ggtt;
> > +     struct i915_ggtt *ggtt = &to_i915(dev)->ggtt;
> >       struct drm_i915_gem_get_aperture *args = data;
> >       struct i915_vma *vma;
> >       u64 pinned;
> >   
> > +     mutex_lock(&ggtt->vm.mutex);
> > +
> >       pinned = ggtt->vm.reserved;
> > -     mutex_lock(&dev->struct_mutex);
> >       list_for_each_entry(vma, &ggtt->vm.bound_list, vm_link)
> >               if (i915_vma_is_pinned(vma))
> >                       pinned += vma->node.size;
> > -     mutex_unlock(&dev->struct_mutex);
> > +
> > +     mutex_unlock(&ggtt->vm.mutex);
> >   
> >       args->aper_size = ggtt->vm.total;
> >       args->aper_available_size = args->aper_size - pinned;
> > @@ -1680,20 +1681,21 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
> >   
> >   static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
> >   {
> > -     struct drm_i915_private *i915;
> > +     struct drm_i915_private *i915 = to_i915(obj->base.dev);
> >       struct list_head *list;
> >       struct i915_vma *vma;
> >   
> >       GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
> >   
> > +     mutex_lock(&i915->ggtt.vm.mutex);
> >       for_each_ggtt_vma(vma, obj) {
> >               if (!drm_mm_node_allocated(&vma->node))
> >                       continue;
> >   
> >               list_move_tail(&vma->vm_link, &vma->vm->bound_list);
> >       }
> > +     mutex_unlock(&i915->ggtt.vm.mutex);
> >   
> > -     i915 = to_i915(obj->base.dev);
> >       spin_lock(&i915->mm.obj_lock);
> >       list = obj->bind_count ? &i915->mm.bound_list : &i915->mm.unbound_list;
> >       list_move_tail(&obj->mm.link, list);
> > diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
> > index 6a3608398d2a..b7c2a396a63f 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_evict.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_evict.c
> > @@ -418,6 +418,7 @@ int i915_gem_evict_vm(struct i915_address_space *vm)
> >       }
> >   
> >       INIT_LIST_HEAD(&eviction_list);
> > +     mutex_lock(&vm->mutex);
> >       list_for_each_entry(vma, &vm->bound_list, vm_link) {
> >               if (i915_vma_is_pinned(vma))
> >                       continue;
> > @@ -425,6 +426,7 @@ int i915_gem_evict_vm(struct i915_address_space *vm)
> >               __i915_vma_pin(vma);
> >               list_add(&vma->evict_link, &eviction_list);
> >       }
> > +     mutex_unlock(&vm->mutex);
> >   
> >       ret = 0;
> >       list_for_each_entry_safe(vma, next, &eviction_list, evict_link) {
> > diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > index e5e23c4ac769..7ae10fbb2ee0 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > @@ -1932,7 +1932,10 @@ static struct i915_vma *pd_vma_create(struct gen6_hw_ppgtt *ppgtt, int size)
> >       vma->ggtt_view.type = I915_GGTT_VIEW_ROTATED; /* prevent fencing */
> >   
> >       INIT_LIST_HEAD(&vma->obj_link);
> > +
> > +     mutex_lock(&vma->vm->mutex);
> >       list_add(&vma->vm_link, &vma->vm->unbound_list);
> > +     mutex_unlock(&vma->vm->mutex);
> >   
> >       return vma;
> >   }
> > @@ -3504,9 +3507,10 @@ void i915_gem_restore_gtt_mappings(struct drm_i915_private *dev_priv)
> >   
> >       i915_check_and_clear_faults(dev_priv);
> >   
> > +     mutex_lock(&ggtt->vm.mutex);
> > +
> >       /* First fill our portion of the GTT with scratch pages */
> >       ggtt->vm.clear_range(&ggtt->vm, 0, ggtt->vm.total);
> > -
> >       ggtt->vm.closed = true; /* skip rewriting PTE on VMA unbind */
> >   
> >       /* clflush objects bound into the GGTT and rebind them. */
> > @@ -3516,19 +3520,26 @@ void i915_gem_restore_gtt_mappings(struct drm_i915_private *dev_priv)
> >               if (!(vma->flags & I915_VMA_GLOBAL_BIND))
> >                       continue;
> >   
> > +             mutex_unlock(&ggtt->vm.mutex);
> > +
> >               if (!i915_vma_unbind(vma))
> 
> What is the model - traverse under the new lock but then no need to get 
> a reference to operate on outside the lock?
> 
> > -                     continue;
> > +                     goto lock;
> >   
> >               WARN_ON(i915_vma_bind(vma,
> >                                     obj ? obj->cache_level : 0,
> >                                     PIN_UPDATE));
> >               if (obj)
> >                       WARN_ON(i915_gem_object_set_to_gtt_domain(obj, false));
> > +
> > +lock:
> > +             mutex_lock(&ggtt->vm.mutex);
> >       }
> >   
> >       ggtt->vm.closed = false;
> >       i915_ggtt_invalidate(dev_priv);
> >   
> > +     mutex_unlock(&ggtt->vm.mutex);
> > +
> >       if (INTEL_GEN(dev_priv) >= 8) {
> >               struct intel_ppat *ppat = &dev_priv->ppat;
> >   
> > diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> > index 95af8cc9fa85..9d04c26c04f9 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> > @@ -490,6 +490,7 @@ i915_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr
> >       }
> >   
> >       /* We also want to clear any cached iomaps as they wrap vmap */
> > +     mutex_lock(&i915->ggtt.vm.mutex);
> >       list_for_each_entry_safe(vma, next,
> >                                &i915->ggtt.vm.bound_list, vm_link) {
> >               unsigned long count = vma->node.size >> PAGE_SHIFT;
> > @@ -497,9 +498,12 @@ i915_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr
> >               if (!vma->iomap || i915_vma_is_active(vma))
> >                       continue;
> >   
> > +             mutex_unlock(&i915->ggtt.vm.mutex);
> >               if (i915_vma_unbind(vma) == 0)
> >                       freed_pages += count;
> > +             mutex_lock(&i915->ggtt.vm.mutex);
> >       }
> > +     mutex_unlock(&i915->ggtt.vm.mutex);
> >   
> >   out:
> >       shrinker_unlock(i915, unlock);
> > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > index 75b97d71f072..21de3a5e9910 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > @@ -703,7 +703,9 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_i915_private *dev_priv
> >       vma->flags |= I915_VMA_GLOBAL_BIND;
> >       __i915_vma_set_map_and_fenceable(vma);
> >   
> > +     mutex_lock(&ggtt->vm.mutex);
> >       list_move_tail(&vma->vm_link, &ggtt->vm.bound_list);
> > +     mutex_unlock(&ggtt->vm.mutex);
> >   
> >       spin_lock(&dev_priv->mm.obj_lock);
> >       list_move_tail(&obj->mm.link, &dev_priv->mm.bound_list);
> > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> > index 7de28baffb8f..dcbd0d345c72 100644
> > --- a/drivers/gpu/drm/i915/i915_vma.c
> > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > @@ -213,7 +213,10 @@ vma_create(struct drm_i915_gem_object *obj,
> >       }
> >       rb_link_node(&vma->obj_node, rb, p);
> >       rb_insert_color(&vma->obj_node, &obj->vma_tree);
> > +
> > +     mutex_lock(&vm->mutex);
> >       list_add(&vma->vm_link, &vm->unbound_list);
> > +     mutex_unlock(&vm->mutex);
> >   
> >       return vma;
> >   
> > @@ -656,7 +659,9 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
> >       GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
> >       GEM_BUG_ON(!i915_gem_valid_gtt_space(vma, cache_level));
> >   
> > +     mutex_lock(&vma->vm->mutex);
> >       list_move_tail(&vma->vm_link, &vma->vm->bound_list);
> > +     mutex_unlock(&vma->vm->mutex);
> >   
> >       if (vma->obj) {
> >               struct drm_i915_gem_object *obj = vma->obj;
> > @@ -689,8 +694,10 @@ i915_vma_remove(struct i915_vma *vma)
> >   
> >       vma->ops->clear_pages(vma);
> >   
> > +     mutex_lock(&vma->vm->mutex);
> >       drm_mm_remove_node(&vma->node);
> >       list_move_tail(&vma->vm_link, &vma->vm->unbound_list);
> > +     mutex_unlock(&vma->vm->mutex);
> >   
> >       /*
> >        * Since the unbound list is global, only move to that list if
> > @@ -802,7 +809,11 @@ static void __i915_vma_destroy(struct i915_vma *vma)
> >       GEM_BUG_ON(i915_gem_active_isset(&vma->last_fence));
> >   
> >       list_del(&vma->obj_link);
> > +
> > +     mutex_lock(&vma->vm->mutex);
> >       list_del(&vma->vm_link);
> > +     mutex_unlock(&vma->vm->mutex);
> > +
> >       if (vma->obj)
> >               rb_erase(&vma->obj_node, &vma->obj->vma_tree);
> >   
> > diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> > index 9d0fe8aac219..eaefba7470f7 100644
> > --- a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> > +++ b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
> > @@ -67,10 +67,13 @@ static int populate_ggtt(struct drm_i915_private *i915)
> >   
> >   static void unpin_ggtt(struct drm_i915_private *i915)
> >   {
> > +     struct i915_ggtt *ggtt = &i915->ggtt;
> >       struct i915_vma *vma;
> >   
> > +     mutex_lock(&ggtt->vm.mutex);
> >       list_for_each_entry(vma, &i915->ggtt.vm.bound_list, vm_link)
> >               i915_vma_unpin(vma);
> > +     mutex_unlock(&ggtt->vm.mutex);
> >   }
> >   
> >   static void cleanup_objects(struct drm_i915_private *i915)
> > diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
> > index 18db008c0c62..850f9eff6029 100644
> > --- a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
> > +++ b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
> > @@ -1237,7 +1237,10 @@ static void track_vma_bind(struct i915_vma *vma)
> >       __i915_gem_object_pin_pages(obj);
> >   
> >       vma->pages = obj->mm.pages;
> > +
> > +     mutex_lock(&vma->vm->mutex);
> >       list_move_tail(&vma->vm_link, &vma->vm->bound_list);
> > +     mutex_unlock(&vma->vm->mutex);
> >   }
> >   
> >   static int exercise_mock(struct drm_i915_private *i915,
> > 
> 
> Why a mutex? Will there be sleeping under it in subsequent patches?

Yeah, we will need to have a wait on GPU under a mutex at some point.
And this is the most likely candidate. Those patches are a bit scarier
and at the last check not deadlock free yet; I think it may need a few
different rules.
-Chris
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