From 484d9a844d0d0aeaa4cd3cec20885b7de9986a55 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 15 Jan 2019 12:44:42 +0000 Subject: [PATCH] drm/i915/userptr: Avoid struct_mutex recursion for mmu_invalidate_range_start 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 by propagating the failure upwards, who can decide themselves to handle it or report it. v2: Mark up the recursive lock behaviour and comment on the various weak points. v3: Follow commit 3824e41975ae ("drm/i915: Use mutex_lock_killable() from inside the shrinker") and also use mutex_lock_killable(). v3.1: No leak on EINTR. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108375 References: 93065ac753e4 ("mm, oom: distinguish blockable mode for mmu notifiers") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190115124442.3500-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_drv.h | 4 +- drivers/gpu/drm/i915/i915_gem.c | 30 +++- drivers/gpu/drm/i915/i915_gem_object.h | 7 + drivers/gpu/drm/i915/i915_gem_userptr.c | 224 ++++++++++++------------ 4 files changed, 139 insertions(+), 126 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 956c1c86f90d..da055a86db4d 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -2935,8 +2935,8 @@ enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */ I915_MM_SHRINKER /* called "recursively" from direct-reclaim-esque */ }; -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 d35dd3d6d3b6..565b2fa1607d 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2303,8 +2303,8 @@ __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); @@ -2328,22 +2328,23 @@ __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; 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; /* May be called by shrinker from within get_pages() (on another bo) */ mutex_lock_nested(&obj->mm.lock, subclass); - if (unlikely(atomic_read(&obj->mm.pages_pin_count))) + if (unlikely(atomic_read(&obj->mm.pages_pin_count))) { + ret = -EBUSY; goto unlock; + } /* * ->put_pages might need to allocate memory for the bit17 swizzle @@ -2351,11 +2352,24 @@ void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj, * lists early. */ pages = __i915_gem_object_unset_pages(obj); + + /* + * XXX Temporary hijinx to avoid updating all backends to handle + * NULL pages. In the future, when we have more asynchronous + * get_pages backends we should be better able to handle the + * cancellation of the async task in a more uniform manner. + */ + if (!pages && !i915_gem_object_needs_async_cancel(obj)) + pages = ERR_PTR(-EINVAL); + 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 ff3da64470dd..cb1b0144d274 100644 --- a/drivers/gpu/drm/i915/i915_gem_object.h +++ b/drivers/gpu/drm/i915/i915_gem_object.h @@ -57,6 +57,7 @@ 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 @@ -387,6 +388,12 @@ 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 1fb6a7bb5054..38e19a42e0f4 100644 --- a/drivers/gpu/drm/i915/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c @@ -49,77 +49,67 @@ 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) +static void add_object(struct i915_mmu_object *mo) { - 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); + GEM_BUG_ON(!RB_EMPTY_NODE(&mo->it.rb)); + interval_tree_insert(&mo->it, &mo->mn->objects); } -static void add_object(struct i915_mmu_object *mo) +static void del_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; + interval_tree_remove(&mo->it, &mo->mn->objects); + RB_CLEAR_NODE(&mo->it.rb); } -static void del_object(struct i915_mmu_object *mo) +static void +__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj, bool value) { - if (!mo->attached) + 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; - interval_tree_remove(&mo->it, &mo->mn->objects); - mo->attached = false; + spin_lock(&mo->mn->lock); + if (value) + add_object(mo); + else + del_object(mo); + spin_unlock(&mo->mn->lock); } -static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn, - const struct mmu_notifier_range *range) +static int +userptr_mn_invalidate_range_start(struct mmu_notifier *_mn, + const struct mmu_notifier_range *range) { 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; unsigned long end; + int ret = 0; if (RB_EMPTY_ROOT(&mn->objects.rb_root)) return 0; @@ -130,11 +120,15 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn, spin_lock(&mn->lock); it = interval_tree_iter_first(&mn->objects, range->start, end); while (it) { + struct drm_i915_gem_object *obj; + if (!range->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 @@ -143,29 +137,65 @@ 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); + obj = container_of(it, struct i915_mmu_object, it)->obj; + if (!kref_get_unless_zero(&obj->base.refcount)) { + it = interval_tree_iter_next(it, range->start, end); + continue; + } + spin_unlock(&mn->lock); + + if (!unlock) { + unlock = &mn->mm->i915->drm.struct_mutex; + + switch (mutex_trylock_recursive(unlock)) { + default: + case MUTEX_TRYLOCK_FAILED: + if (!mutex_lock_killable_nested(unlock, I915_MM_SHRINKER)) { + i915_gem_object_put(obj); + return -EINTR; + } + /* fall through */ + case MUTEX_TRYLOCK_SUCCESS: + break; + + case MUTEX_TRYLOCK_RECURSIVE: + unlock = ERR_PTR(-EEXIST); + break; + } + } + + 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; - list_add(&mo->link, &cancelled); - it = interval_tree_iter_next(it, range->start, end); + spin_lock(&mn->lock); + + /* + * As we do not (yet) protect the mmu from concurrent insertion + * over this range, there is no guarantee that this search will + * terminate given a pathologic workload. + */ + it = interval_tree_iter_first(&mn->objects, range->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 = { - .invalidate_range_start = i915_gem_userptr_mn_invalidate_range_start, + .invalidate_range_start = userptr_mn_invalidate_range_start, }; 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; @@ -176,13 +206,7 @@ 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; } @@ -192,16 +216,14 @@ 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 * @@ -214,7 +236,7 @@ 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); @@ -237,10 +259,8 @@ 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; } @@ -263,14 +283,14 @@ 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; @@ -284,12 +304,16 @@ 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) { @@ -458,42 +482,6 @@ alloc_table: 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) { @@ -679,8 +667,11 @@ 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; @@ -718,7 +709,8 @@ 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, -- 2.30.2