Re: [Intel-gfx] [PATCH v9 17/70] drm/i915: Flatten obj->mm.lock

On Tue, Mar 23, 2021 at 04:50:06PM +0100, Maarten Lankhorst wrote:

With userptr fixed, there is no need for all separate lockdep classes now, and we can remove all lockdep tricks used. A trylock in the shrinker is all we need now to flatten the locking hierarchy.

Signed-off-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Reviewed-by: Thomas Hellström thomas.hellstrom@linux.intel.com

Minor conflict with this one here when applying, due to lack of

https://lore.kernel.org/intel-gfx/20210202154318.19246-1-chris@chris-wilson.....

It's not a bad idea, but if we do this we really should move this helper into the right headers, and ideally get linux-mm/-fs folks to ack this as a good idea. Especially Dave Chinner very much wants to be in the loop for anything that touches fs_reclaim lockdep annotations. -Daniel

---

drivers/gpu/drm/i915/gem/i915_gem_object.c | 5 +-- drivers/gpu/drm/i915/gem/i915_gem_object.h | 20 ++---------- drivers/gpu/drm/i915/gem/i915_gem_pages.c | 34 ++++++++++---------- drivers/gpu/drm/i915/gem/i915_gem_phys.c | 2 +- drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 10 +++--- drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 2 +- 6 files changed, 27 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c index 6083b9c14be6..821cb40f8d73 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -62,7 +62,7 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj, const struct drm_i915_gem_object_ops *ops, struct lock_class_key *key, unsigned flags) {

• __mutex_init(&obj->mm.lock, ops->name ?: "obj->mm.lock", key);

• mutex_init(&obj->mm.lock);

  spin_lock_init(&obj->vma.lock); INIT_LIST_HEAD(&obj->vma.list);

@@ -86,9 +86,6 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj, mutex_init(&obj->mm.get_page.lock); INIT_RADIX_TREE(&obj->mm.get_dma_page.radix, GFP_KERNEL | __GFP_NOWARN); mutex_init(&obj->mm.get_dma_page.lock);

• if (IS_ENABLED(CONFIG_LOCKDEP) && i915_gem_object_is_shrinkable(obj))

• fs_reclaim_taints_mutex(&obj->mm.lock);
  

}

/** diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h index b5af9c440ac5..a0e1c4ff0de4 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h @@ -372,27 +372,10 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj, int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj); int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj);

-enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */

• I915_MM_NORMAL = 0,
• /*

• * Only used by struct_mutex, when called "recursively" from
  

• * direct-reclaim-esque. Safe because there is only every one
  

• * struct_mutex in the entire system.
  

• */
  

• I915_MM_SHRINKER = 1,
• /*

• * Used for obj->mm.lock when allocating pages. Safe because the object
  

• * isn't yet on any LRU, and therefore the shrinker can't deadlock on
  

• * it. As soon as the object has pages, obj->mm.lock nests within
  

• * fs_reclaim.
  

• */
  

• I915_MM_GET_PAGES = 1,

-};

static inline int __must_check i915_gem_object_pin_pages(struct drm_i915_gem_object *obj) {

• might_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);

• might_lock(&obj->mm.lock);

  if (atomic_inc_not_zero(&obj->mm.pages_pin_count)) return 0;

@@ -436,6 +419,7 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj) }

int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj); +int __i915_gem_object_put_pages_locked(struct drm_i915_gem_object *obj); void i915_gem_object_truncate(struct drm_i915_gem_object *obj); void i915_gem_object_writeback(struct drm_i915_gem_object *obj);

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c index e7d7650072c5..e947d4c0da1f 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c @@ -114,7 +114,7 @@ int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj) { int err;

• err = mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES);

• err = mutex_lock_interruptible(&obj->mm.lock); if (err) return err;

@@ -196,21 +196,13 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj) return pages; }

-int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj) +int __i915_gem_object_put_pages_locked(struct drm_i915_gem_object *obj) { struct sg_table *pages;

• int err;

  if (i915_gem_object_has_pinned_pages(obj)) return -EBUSY;

• /* May be called by shrinker from within get_pages() (on another bo) */

• mutex_lock(&obj->mm.lock);

• if (unlikely(atomic_read(&obj->mm.pages_pin_count))) {

• err = -EBUSY;
  

• goto unlock;
  

• }

• i915_gem_object_release_mmap_offset(obj);

  /*

@@ -226,14 +218,22 @@ int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj) * get_pages backends we should be better able to handle the * cancellation of the async task in a more uniform manner. */

• if (!pages)

• pages = ERR_PTR(-EINVAL);
  

• if (!IS_ERR(pages))

• if (!IS_ERR_OR_NULL(pages)) obj->ops->put_pages(obj, pages);

• err = 0;

-unlock:

• return 0;

+}

+int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj) +{

• int err;

• if (i915_gem_object_has_pinned_pages(obj))

• return -EBUSY;
  

• /* May be called by shrinker from within get_pages() (on another bo) */

• mutex_lock(&obj->mm.lock);

• err = __i915_gem_object_put_pages_locked(obj); mutex_unlock(&obj->mm.lock);

  return err;

@@ -341,7 +341,7 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj, !i915_gem_object_type_has(obj, I915_GEM_OBJECT_HAS_IOMEM)) return ERR_PTR(-ENXIO);

• err = mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES);

• err = mutex_lock_interruptible(&obj->mm.lock); if (err) return ERR_PTR(err);

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c b/drivers/gpu/drm/i915/gem/i915_gem_phys.c index 06c481ff79d8..44329c435cf1 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c @@ -236,7 +236,7 @@ int i915_gem_object_attach_phys(struct drm_i915_gem_object *obj, int align) if (err) return err;

• err = mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES);

• err = mutex_lock_interruptible(&obj->mm.lock); if (err) goto err_unlock;

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c index b64a0788381f..3052ef5ad89d 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c @@ -49,9 +49,9 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj, flags = I915_GEM_OBJECT_UNBIND_TEST;

if (i915_gem_object_unbind(obj, flags) == 0)

• __i915_gem_object_put_pages(obj);
  

• return true;
  
  

• return !i915_gem_object_has_pages(obj);

• return false;

}

static void try_to_writeback(struct drm_i915_gem_object *obj, @@ -200,10 +200,10 @@ i915_gem_shrink(struct drm_i915_private *i915,

	spin_unlock_irqrestore(&i915->mm.obj_lock, flags);

• 	if (unsafe_drop_pages(obj, shrink)) {
  

• 	if (unsafe_drop_pages(obj, shrink) &&
  

• 	    mutex_trylock(&obj->mm.lock)) {
  	/* May arrive from get_pages on another bo */
  

• 		mutex_lock(&obj->mm.lock);
  

• 		if (!i915_gem_object_has_pages(obj)) {
  

• 		if (!__i915_gem_object_put_pages_locked(obj)) {
  		try_to_writeback(obj, shrink);
  		count += obj->base.size >> PAGE_SHIFT;
  	}
  

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c index 1e42fbc68697..503325e74eff 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c @@ -253,7 +253,7 @@ static int i915_gem_object_userptr_unbind(struct drm_i915_gem_object *obj, bool if (GEM_WARN_ON(i915_gem_object_has_pinned_pages(obj))) return -EBUSY;

• mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);

• mutex_lock(&obj->mm.lock);

  pages = __i915_gem_object_unset_pages(obj); if (!IS_ERR_OR_NULL(pages))

-- 2.31.0

---

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