On 02/11/2018 16:12, Chris Wilson wrote:
Since commit 93065ac753e4 ("mm, oom: distinguish blockable mode for mmu
notifiers") we have been able to report failure from
mmu_invalidate_range_start which allows us to use a trylock on the
struct_mutex to avoid potential recursion and report -EBUSY instead.
Furthermore, this allows us to pull the work into the main callback and
avoid the sleight-of-hand in using a workqueue to avoid lockdep.
However, not all paths to mmu_invalidate_range_start are prepared to
handle failure, so instead of reporting the recursion, deal with it.
Judging by the code below non-blockable paths can handle failure but
blockable can not? Right, now that I read the invalidate_range_start api
docs that seems to be the case. So that sounds like blockable brings us
marginal benefits, if any, on the design level. Which is why I suppose
this patch looks quite big. Lets see..
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108375
References: 93065ac753e4 ("mm, oom: distinguish blockable moe for mmu notifiers")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_drv.h | 4 +-
drivers/gpu/drm/i915/i915_gem.c | 18 +-
drivers/gpu/drm/i915/i915_gem_object.h | 7 +
drivers/gpu/drm/i915/i915_gem_userptr.c | 217 +++++++++++-------------
4 files changed, 120 insertions(+), 126 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2a88a7eb871b..1056b12c3bc8 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3073,8 +3073,8 @@ enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock */
I915_MM_SHRINKER
};
-void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
- enum i915_mm_subclass subclass);
+int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
+ enum i915_mm_subclass subclass);
void __i915_gem_object_invalidate(struct drm_i915_gem_object *obj);
enum i915_map_type {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 93d09282710d..9a8af9454a53 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2429,8 +2429,8 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
struct sg_table *pages;
pages = fetch_and_zero(&obj->mm.pages);
- if (!pages)
- return NULL;
+ if (IS_ERR_OR_NULL(pages))
+ return pages; >
spin_lock(&i915->mm.obj_lock);
list_del(&obj->mm.link);
@@ -2454,17 +2454,16 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
return pages;
}
-void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
- enum i915_mm_subclass subclass)
+int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
+ enum i915_mm_subclass subclass)
{
struct sg_table *pages;
+ int ret = -EBUSY;
if (i915_gem_object_has_pinned_pages(obj))
- return;
+ return -EBUSY;
GEM_BUG_ON(obj->bind_count);
- if (!i915_gem_object_has_pages(obj))
- return;
Unrelated to this patch?
/* May be called by shrinker from within get_pages() (on another bo) */
mutex_lock_nested(&obj->mm.lock, subclass);
@@ -2477,11 +2476,16 @@ void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
* lists early.
*/
pages = __i915_gem_object_unset_pages(obj);
+ if (!pages && !i915_gem_object_needs_async_cancel(obj))
+ pages = ERR_PTR(-EINVAL);
(Hmm yeah, this path did not used to handle the existing possible NULL
pages here.)
Please put a blurb in the commit message on the high to medium level
design of the change.
if (!IS_ERR(pages))
obj->ops->put_pages(obj, pages);
+ ret = 0;
unlock:
mutex_unlock(&obj->mm.lock);
+
+ return ret;
}
bool i915_sg_trim(struct sg_table *orig_st)
diff --git a/drivers/gpu/drm/i915/i915_gem_object.h b/drivers/gpu/drm/i915/i915_gem_object.h
index a6dd7c46de0d..49ce797173b5 100644
--- a/drivers/gpu/drm/i915/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/i915_gem_object.h
@@ -56,6 +56,7 @@ struct drm_i915_gem_object_ops {
#define I915_GEM_OBJECT_HAS_STRUCT_PAGE BIT(0)
#define I915_GEM_OBJECT_IS_SHRINKABLE BIT(1)
#define I915_GEM_OBJECT_IS_PROXY BIT(2)
+#define I915_GEM_OBJECT_ASYNC_CANCEL BIT(3)
/* Interface between the GEM object and its backing storage.
* get_pages() is called once prior to the use of the associated set
@@ -386,6 +387,12 @@ i915_gem_object_is_proxy(const struct drm_i915_gem_object *obj)
return obj->ops->flags & I915_GEM_OBJECT_IS_PROXY;
}
+static inline bool
+i915_gem_object_needs_async_cancel(const struct drm_i915_gem_object *obj)
+{
+ return obj->ops->flags & I915_GEM_OBJECT_ASYNC_CANCEL;
+}
+
static inline bool
i915_gem_object_is_active(const struct drm_i915_gem_object *obj)
{
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 2c9b284036d1..ab5ae426e27b 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -50,79 +50,84 @@ struct i915_mmu_notifier {
struct hlist_node node;
struct mmu_notifier mn;
struct rb_root_cached objects;
- struct workqueue_struct *wq;
+ struct i915_mm_struct *mm;
};
struct i915_mmu_object {
struct i915_mmu_notifier *mn;
struct drm_i915_gem_object *obj;
struct interval_tree_node it;
- struct list_head link;
- struct work_struct work;
- bool attached;
};
-static void cancel_userptr(struct work_struct *work)
-{
- struct i915_mmu_object *mo = container_of(work, typeof(*mo), work);
- struct drm_i915_gem_object *obj = mo->obj;
- struct work_struct *active;
-
- /* Cancel any active worker and force us to re-evaluate gup */
- mutex_lock(&obj->mm.lock);
- active = fetch_and_zero(&obj->userptr.work);
- mutex_unlock(&obj->mm.lock);
- if (active)
- goto out;
-
- i915_gem_object_wait(obj, I915_WAIT_ALL, MAX_SCHEDULE_TIMEOUT, NULL);
-
- mutex_lock(&obj->base.dev->struct_mutex);
-
- /* We are inside a kthread context and can't be interrupted */
- if (i915_gem_object_unbind(obj) == 0)
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
- WARN_ONCE(i915_gem_object_has_pages(obj),
- "Failed to release pages: bind_count=%d, pages_pin_count=%d, pin_global=%d\n",
- obj->bind_count,
- atomic_read(&obj->mm.pages_pin_count),
- obj->pin_global);
-
- mutex_unlock(&obj->base.dev->struct_mutex);
-
-out:
- i915_gem_object_put(obj);
-}
-
static void add_object(struct i915_mmu_object *mo)
{
- if (mo->attached)
+ if (!RB_EMPTY_NODE(&mo->it.rb))
return;
interval_tree_insert(&mo->it, &mo->mn->objects);
- mo->attached = true;
}
static void del_object(struct i915_mmu_object *mo)
{
- if (!mo->attached)
+ if (RB_EMPTY_NODE(&mo->it.rb))
return;
interval_tree_remove(&mo->it, &mo->mn->objects);
- mo->attached = false;
+ RB_CLEAR_NODE(&mo->it.rb);
+}
+
+static void
+__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj, bool value)
+{
+ struct i915_mmu_object *mo = obj->userptr.mmu_object;
+
+ /*
+ * During mm_invalidate_range we need to cancel any userptr that
+ * overlaps the range being invalidated. Doing so requires the
+ * struct_mutex, and that risks recursion. In order to cause
+ * recursion, the user must alias the userptr address space with
+ * a GTT mmapping (possible with a MAP_FIXED) - then when we have
+ * to invalidate that mmaping, mm_invalidate_range is called with
+ * the userptr address *and* the struct_mutex held. To prevent that
+ * we set a flag under the i915_mmu_notifier spinlock to indicate
+ * whether this object is valid.
+ */
+ if (!mo)
+ return;
+
+ spin_lock(&mo->mn->lock);
+ if (value)
+ add_object(mo);
+ else
+ del_object(mo);
+ spin_unlock(&mo->mn->lock);
+}
+
+static struct mutex *__i915_mutex_lock_recursive(struct mutex *m)
+{
+ switch (mutex_trylock_recursive(m)) {
+ default:
+ case MUTEX_TRYLOCK_FAILED:
+ mutex_lock(m);
+ case MUTEX_TRYLOCK_SUCCESS:
+ return m;
+
+ case MUTEX_TRYLOCK_RECURSIVE:
+ return ERR_PTR(-EEXIST);
This suggest we will break the api requirement to return always
invalidate in the blockable case.
+ }
}
static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
- struct mm_struct *mm,
- unsigned long start,
- unsigned long end,
- bool blockable)
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end,
+ bool blockable)
{
struct i915_mmu_notifier *mn =
container_of(_mn, struct i915_mmu_notifier, mn);
- struct i915_mmu_object *mo;
struct interval_tree_node *it;
- LIST_HEAD(cancelled);
+ struct mutex *unlock = NULL;
+ int ret = 0;
if (RB_EMPTY_ROOT(&mn->objects.rb_root))
return 0;
@@ -133,11 +138,15 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
spin_lock(&mn->lock);
it = interval_tree_iter_first(&mn->objects, start, end);
while (it) {
+ struct drm_i915_gem_object *obj;
+
if (!blockable) {
- spin_unlock(&mn->lock);
- return -EAGAIN;
+ ret = -EAGAIN;
+ break;
}
- /* The mmu_object is released late when destroying the
+
+ /*
+ * The mmu_object is released late when destroying the
* GEM object so it is entirely possible to gain a
* reference on an object in the process of being freed
* since our serialisation is via the spinlock and not
@@ -146,21 +155,33 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
* use-after-free we only acquire a reference on the
* object if it is not in the process of being destroyed.
*/
- mo = container_of(it, struct i915_mmu_object, it);
- if (kref_get_unless_zero(&mo->obj->base.refcount))
- queue_work(mn->wq, &mo->work);
-
- list_add(&mo->link, &cancelled);
- it = interval_tree_iter_next(it, start, end);
+ obj = container_of(it, struct i915_mmu_object, it)->obj;
+ if (!kref_get_unless_zero(&obj->base.refcount)) {
+ it = interval_tree_iter_next(it, start, end);
+ continue;
+ }
+ spin_unlock(&mn->lock);
+
+ if (!unlock)
+ unlock = __i915_mutex_lock_recursive(&mn->mm->i915->drm.struct_mutex);
Hmm .. but we proceed regardless of the trylock result and don't even
bother looking at it. I don't get it. I stop here since it doesn't make
sense to me at this moment.
Regards,
Tvrtko
+ ret = i915_gem_object_unbind(obj);
+ if (ret == 0)
+ ret = __i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
+ i915_gem_object_put(obj);
+ if (ret)
+ goto unlock;
+
+ spin_lock(&mn->lock);
+ it = interval_tree_iter_first(&mn->objects, start, end);
}
- list_for_each_entry(mo, &cancelled, link)
- del_object(mo);
spin_unlock(&mn->lock);
- if (!list_empty(&cancelled))
- flush_workqueue(mn->wq);
+unlock:
+ if (!IS_ERR_OR_NULL(unlock))
+ mutex_unlock(unlock);
+
+ return ret;
- return 0;
}
static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
@@ -168,7 +189,7 @@ static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
};
static struct i915_mmu_notifier *
-i915_mmu_notifier_create(struct mm_struct *mm)
+i915_mmu_notifier_create(struct i915_mm_struct *mm)
{
struct i915_mmu_notifier *mn;
@@ -179,13 +200,7 @@ i915_mmu_notifier_create(struct mm_struct *mm)
spin_lock_init(&mn->lock);
mn->mn.ops = &i915_gem_userptr_notifier;
mn->objects = RB_ROOT_CACHED;
- mn->wq = alloc_workqueue("i915-userptr-release",
- WQ_UNBOUND | WQ_MEM_RECLAIM,
- 0);
- if (mn->wq == NULL) {
- kfree(mn);
- return ERR_PTR(-ENOMEM);
- }
+ mn->mm = mm;
return mn;
}
@@ -195,16 +210,14 @@ i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
{
struct i915_mmu_object *mo;
- mo = obj->userptr.mmu_object;
- if (mo == NULL)
+ mo = fetch_and_zero(&obj->userptr.mmu_object);
+ if (!mo)
return;
spin_lock(&mo->mn->lock);
del_object(mo);
spin_unlock(&mo->mn->lock);
kfree(mo);
-
- obj->userptr.mmu_object = NULL;
}
static struct i915_mmu_notifier *
@@ -217,7 +230,7 @@ i915_mmu_notifier_find(struct i915_mm_struct *mm)
if (mn)
return mn;
- mn = i915_mmu_notifier_create(mm->mm);
+ mn = i915_mmu_notifier_create(mm);
if (IS_ERR(mn))
err = PTR_ERR(mn);
@@ -240,10 +253,8 @@ i915_mmu_notifier_find(struct i915_mm_struct *mm)
mutex_unlock(&mm->i915->mm_lock);
up_write(&mm->mm->mmap_sem);
- if (mn && !IS_ERR(mn)) {
- destroy_workqueue(mn->wq);
+ if (mn && !IS_ERR(mn))
kfree(mn);
- }
return err ? ERR_PTR(err) : mm->mn;
}
@@ -266,14 +277,14 @@ i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
return PTR_ERR(mn);
mo = kzalloc(sizeof(*mo), GFP_KERNEL);
- if (mo == NULL)
+ if (!mo)
return -ENOMEM;
mo->mn = mn;
mo->obj = obj;
mo->it.start = obj->userptr.ptr;
mo->it.last = obj->userptr.ptr + obj->base.size - 1;
- INIT_WORK(&mo->work, cancel_userptr);
+ RB_CLEAR_NODE(&mo->it.rb);
obj->userptr.mmu_object = mo;
return 0;
@@ -287,12 +298,16 @@ i915_mmu_notifier_free(struct i915_mmu_notifier *mn,
return;
mmu_notifier_unregister(&mn->mn, mm);
- destroy_workqueue(mn->wq);
kfree(mn);
}
#else
+static void
+__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj, bool value)
+{
+}
+
static void
i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
{
@@ -461,42 +476,6 @@ __i915_gem_userptr_alloc_pages(struct drm_i915_gem_object *obj,
return st;
}
-static int
-__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj,
- bool value)
-{
- int ret = 0;
-
- /* During mm_invalidate_range we need to cancel any userptr that
- * overlaps the range being invalidated. Doing so requires the
- * struct_mutex, and that risks recursion. In order to cause
- * recursion, the user must alias the userptr address space with
- * a GTT mmapping (possible with a MAP_FIXED) - then when we have
- * to invalidate that mmaping, mm_invalidate_range is called with
- * the userptr address *and* the struct_mutex held. To prevent that
- * we set a flag under the i915_mmu_notifier spinlock to indicate
- * whether this object is valid.
- */
-#if defined(CONFIG_MMU_NOTIFIER)
- if (obj->userptr.mmu_object == NULL)
- return 0;
-
- spin_lock(&obj->userptr.mmu_object->mn->lock);
- /* In order to serialise get_pages with an outstanding
- * cancel_userptr, we must drop the struct_mutex and try again.
- */
- if (!value)
- del_object(obj->userptr.mmu_object);
- else if (!work_pending(&obj->userptr.mmu_object->work))
- add_object(obj->userptr.mmu_object);
- else
- ret = -EAGAIN;
- spin_unlock(&obj->userptr.mmu_object->mn->lock);
-#endif
-
- return ret;
-}
-
static void
__i915_gem_userptr_get_pages_worker(struct work_struct *_work)
{
@@ -682,8 +661,11 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
struct sgt_iter sgt_iter;
struct page *page;
- BUG_ON(obj->userptr.work != NULL);
+ /* Cancel any inflight work and force them to restart their gup */
+ obj->userptr.work = NULL;
__i915_gem_userptr_set_active(obj, false);
+ if (!pages)
+ return;
if (obj->mm.madv != I915_MADV_WILLNEED)
obj->mm.dirty = false;
@@ -721,7 +703,8 @@ i915_gem_userptr_dmabuf_export(struct drm_i915_gem_object *obj)
static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
.flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE |
- I915_GEM_OBJECT_IS_SHRINKABLE,
+ I915_GEM_OBJECT_IS_SHRINKABLE |
+ I915_GEM_OBJECT_ASYNC_CANCEL,
.get_pages = i915_gem_userptr_get_pages,
.put_pages = i915_gem_userptr_put_pages,
.dmabuf_export = i915_gem_userptr_dmabuf_export,
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