[Intel-gfx] [PATCH 2/2] drm/i915/gem: Avoid kmalloc under i915->mm_lock
Chris Wilson
chris at chris-wilson.co.uk
Fri Jun 5 10:56:46 UTC 2020
Rearrange the allocation of the mm_struct registration to avoid
allocating underneath the i915->mm_lock, so that we avoid tainting the
lock (and in turn many other locks that may be held as i915->mm_lock is
taken, and those locks we may want on the free [shrinker] paths). In
doing so, we convert the lookup to be RCU protected by courtesy of
converting the free-worker to be an rcu_work.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 123 +++++++++-----------
drivers/gpu/drm/i915/i915_drv.h | 2 +-
2 files changed, 59 insertions(+), 66 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 2adc0ea429fb..3dd2bbb37577 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -21,7 +21,7 @@ struct i915_mm_struct {
struct i915_mmu_notifier *mn;
struct hlist_node node;
struct kref kref;
- struct work_struct work;
+ struct rcu_work work;
};
#if defined(CONFIG_MMU_NOTIFIER)
@@ -189,40 +189,31 @@ i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
static struct i915_mmu_notifier *
i915_mmu_notifier_find(struct i915_mm_struct *mm)
{
- struct i915_mmu_notifier *mn;
- int err = 0;
+ struct i915_mmu_notifier *mn, *old;
+ int err;
- mn = mm->mn;
- if (mn)
+ mn = READ_ONCE(mm->mn);
+ if (likely(mn))
return mn;
mn = i915_mmu_notifier_create(mm);
if (IS_ERR(mn))
- err = PTR_ERR(mn);
-
- down_write(&mm->mm->mmap_sem);
- mutex_lock(&mm->i915->mm_lock);
- if (mm->mn == NULL && !err) {
- /* Protected by mmap_sem (write-lock) */
- err = __mmu_notifier_register(&mn->mn, mm->mm);
- if (!err) {
- /* Protected by mm_lock */
- mm->mn = fetch_and_zero(&mn);
- }
- } else if (mm->mn) {
- /*
- * Someone else raced and successfully installed the mmu
- * notifier, we can cancel our own errors.
- */
- err = 0;
+ return mn;
+
+ err = mmu_notifier_register(&mn->mn, mm->mm);
+ if (err) {
+ kfree(mn);
+ return ERR_PTR(err);
}
- mutex_unlock(&mm->i915->mm_lock);
- up_write(&mm->mm->mmap_sem);
- if (mn && !IS_ERR(mn))
+ old = cmpxchg(&mm->mn, NULL, mn);
+ if (old) {
+ mmu_notifier_unregister(&mn->mn, mm->mm);
kfree(mn);
+ mn = old;
+ }
- return err ? ERR_PTR(err) : mm->mn;
+ return mn;
}
static int
@@ -301,23 +292,26 @@ i915_mmu_notifier_free(struct i915_mmu_notifier *mn,
#endif
static struct i915_mm_struct *
-__i915_mm_struct_find(struct drm_i915_private *dev_priv, struct mm_struct *real)
+__i915_mm_struct_find(struct drm_i915_private *i915, struct mm_struct *real)
{
- struct i915_mm_struct *mm;
+ struct i915_mm_struct *it, *mm = NULL;
- /* Protected by dev_priv->mm_lock */
- hash_for_each_possible(dev_priv->mm_structs, mm, node, (unsigned long)real)
- if (mm->mm == real)
- return mm;
+ rcu_read_lock();
+ hash_for_each_possible(i915->mm_structs, it, node, (unsigned long)real)
+ if (it->mm == real && kref_get_unless_zero(&it->kref)) {
+ mm = it;
+ break;
+ }
+ rcu_read_unlock();
- return NULL;
+ return mm;
}
static int
i915_gem_userptr_init__mm_struct(struct drm_i915_gem_object *obj)
{
- struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
- struct i915_mm_struct *mm;
+ struct drm_i915_private *i915 = to_i915(obj->base.dev);
+ struct i915_mm_struct *mm, *new;
int ret = 0;
/* During release of the GEM object we hold the struct_mutex. This
@@ -330,39 +324,40 @@ i915_gem_userptr_init__mm_struct(struct drm_i915_gem_object *obj)
* struct_mutex, i.e. we need to schedule a worker to do the clean
* up.
*/
- mutex_lock(&dev_priv->mm_lock);
- mm = __i915_mm_struct_find(dev_priv, current->mm);
- if (mm == NULL) {
- mm = kmalloc(sizeof(*mm), GFP_KERNEL);
- if (mm == NULL) {
- ret = -ENOMEM;
- goto out;
- }
+ mm = __i915_mm_struct_find(i915, current->mm);
+ if (mm)
+ goto out;
- kref_init(&mm->kref);
- mm->i915 = to_i915(obj->base.dev);
-
- mm->mm = current->mm;
- mmgrab(current->mm);
+ new = kmalloc(sizeof(*mm), GFP_KERNEL);
+ if (new == NULL)
+ return -ENOMEM;
- mm->mn = NULL;
+ kref_init(&new->kref);
+ new->i915 = to_i915(obj->base.dev);
+ new->mm = current->mm;
+ new->mn = NULL;
- /* Protected by dev_priv->mm_lock */
- hash_add(dev_priv->mm_structs,
- &mm->node, (unsigned long)mm->mm);
- } else
- kref_get(&mm->kref);
+ spin_lock(&i915->mm_lock);
+ mm = __i915_mm_struct_find(i915, current->mm);
+ if (!mm) {
+ hash_add(i915->mm_structs, &new->node, (unsigned long)new->mm);
+ mmgrab(current->mm);
+ mm = new;
+ }
+ spin_unlock(&i915->mm_lock);
+ if (mm != new)
+ kfree(new);
- obj->userptr.mm = mm;
out:
- mutex_unlock(&dev_priv->mm_lock);
+ obj->userptr.mm = mm;
return ret;
}
static void
__i915_mm_struct_free__worker(struct work_struct *work)
{
- struct i915_mm_struct *mm = container_of(work, typeof(*mm), work);
+ struct i915_mm_struct *mm = container_of(work, typeof(*mm), work.work);
+
i915_mmu_notifier_free(mm->mn, mm->mm);
mmdrop(mm->mm);
kfree(mm);
@@ -373,12 +368,12 @@ __i915_mm_struct_free(struct kref *kref)
{
struct i915_mm_struct *mm = container_of(kref, typeof(*mm), kref);
- /* Protected by dev_priv->mm_lock */
+ spin_lock(&mm->i915->mm_lock);
hash_del(&mm->node);
- mutex_unlock(&mm->i915->mm_lock);
+ spin_unlock(&mm->i915->mm_lock);
- INIT_WORK(&mm->work, __i915_mm_struct_free__worker);
- queue_work(mm->i915->mm.userptr_wq, &mm->work);
+ INIT_RCU_WORK(&mm->work, __i915_mm_struct_free__worker);
+ queue_rcu_work(mm->i915->mm.userptr_wq, &mm->work);
}
static void
@@ -387,9 +382,7 @@ i915_gem_userptr_release__mm_struct(struct drm_i915_gem_object *obj)
if (obj->userptr.mm == NULL)
return;
- kref_put_mutex(&obj->userptr.mm->kref,
- __i915_mm_struct_free,
- &to_i915(obj->base.dev)->mm_lock);
+ kref_put(&obj->userptr.mm->kref, __i915_mm_struct_free);
obj->userptr.mm = NULL;
}
@@ -839,7 +832,7 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
int i915_gem_init_userptr(struct drm_i915_private *dev_priv)
{
- mutex_init(&dev_priv->mm_lock);
+ spin_lock_init(&dev_priv->mm_lock);
hash_init(dev_priv->mm_structs);
dev_priv->mm.userptr_wq =
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5649f8e502fe..7464656253c9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -988,7 +988,7 @@ struct drm_i915_private {
struct i915_gem_mm mm;
DECLARE_HASHTABLE(mm_structs, 7);
- struct mutex mm_lock;
+ spinlock_t mm_lock;
/* Kernel Modesetting */
--
2.20.1
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