@@ -191,7 +191,7 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
GEM_BUG_ON(!list_empty(&obj->lut_list));
atomic_set(&obj->mm.pages_pin_count, 0);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
GEM_BUG_ON(i915_gem_object_has_pages(obj));
bitmap_free(obj->bit_17);
@@ -281,11 +281,21 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */
I915_MM_NORMAL = 0,
- I915_MM_SHRINKER /* called "recursively" from direct-reclaim-esque */
+ /*
+ * 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,
};
-int __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);
void i915_gem_object_truncate(struct drm_i915_gem_object *obj);
void i915_gem_object_writeback(struct drm_i915_gem_object *obj);
@@ -157,7 +157,15 @@ struct drm_i915_gem_object {
unsigned int pin_global;
struct {
- struct mutex lock; /* protects the pages and their use */
+ /*
+ * Protects the pages and their use.
+ *
+ * IMPORTANT: It is not allowed to allocate memory while holding
+ * this lock, because the shrinker might recurse on it, except
+ * when there are no pages allocated yet and the object isn't
+ * visible on any LRU.
+ */
+ struct mutex lock;
atomic_t pages_pin_count;
struct sg_table *pages;
@@ -101,7 +101,7 @@ int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
{
int err;
- err = mutex_lock_interruptible(&obj->mm.lock);
+ err = mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES);
if (err)
return err;
@@ -179,8 +179,7 @@ __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,
- enum i915_mm_subclass subclass)
+int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
{
struct sg_table *pages;
int err;
@@ -191,7 +190,7 @@ int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
GEM_BUG_ON(atomic_read(&obj->bind_count));
/* May be called by shrinker from within get_pages() (on another bo) */
- mutex_lock_nested(&obj->mm.lock, subclass);
+ mutex_lock(&obj->mm.lock);
if (unlikely(atomic_read(&obj->mm.pages_pin_count))) {
err = -EBUSY;
goto unlock;
@@ -285,7 +284,7 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
if (unlikely(!i915_gem_object_has_struct_page(obj)))
return ERR_PTR(-ENXIO);
- err = mutex_lock_interruptible(&obj->mm.lock);
+ err = mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES);
if (err)
return ERR_PTR(err);
@@ -156,7 +156,7 @@ int i915_gem_object_attach_phys(struct drm_i915_gem_object *obj, int align)
if (err)
return err;
- mutex_lock(&obj->mm.lock);
+ mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
if (obj->mm.madv != I915_MADV_WILLNEED) {
err = -EFAULT;
@@ -98,7 +98,7 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj,
flags = I915_GEM_OBJECT_UNBIND_ACTIVE;
if (i915_gem_object_unbind(obj, flags) == 0)
- __i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
+ __i915_gem_object_put_pages(obj);
return !i915_gem_object_has_pages(obj);
}
@@ -254,8 +254,7 @@ i915_gem_shrink(struct drm_i915_private *i915,
if (unsafe_drop_pages(obj, shrink)) {
/* May arrive from get_pages on another bo */
- mutex_lock_nested(&obj->mm.lock,
- I915_MM_SHRINKER);
+ mutex_lock(&obj->mm.lock);
if (!i915_gem_object_has_pages(obj)) {
try_to_writeback(obj, shrink);
count += obj->base.size >> PAGE_SHIFT;
@@ -158,7 +158,7 @@ userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
ret = i915_gem_object_unbind(obj,
I915_GEM_OBJECT_UNBIND_ACTIVE);
if (ret == 0)
- ret = __i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
+ ret = __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
if (ret)
goto unlock;
@@ -562,7 +562,7 @@ static int igt_mock_ppgtt_misaligned_dma(void *arg)
i915_vma_close(vma);
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
@@ -590,7 +590,7 @@ static void close_object_list(struct list_head *objects,
list_del(&obj->st_link);
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
}
@@ -860,7 +860,7 @@ static int igt_mock_ppgtt_64K(void *arg)
i915_vma_close(vma);
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
}
@@ -1268,7 +1268,7 @@ static int igt_ppgtt_exhaust_huge(void *arg)
}
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
}
@@ -1330,7 +1330,7 @@ static int igt_ppgtt_internal_huge(void *arg)
}
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
@@ -1399,7 +1399,7 @@ static int igt_ppgtt_gemfs_huge(void *arg)
}
i915_gem_object_unpin_pages(obj);
- __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
+ __i915_gem_object_put_pages(obj);
i915_gem_object_put(obj);
}
The trouble with having a plain nesting flag for locks which do not naturally nest (unlike block devices and their partitions, which is the original motivation for nesting levels) is that lockdep will never spot a true deadlock if you screw up. This patch is an attempt at trying better, by highlighting a bit more the actual nature of the nesting that's going on. Essentially we have two kinds of objects: - objects without pages allocated, which cannot be on any lru and are hence inaccessible to the shrinker. - objects which have pages allocated, which are on an lru, and which the shrinker can decide to throw out. For the former type of object, memory allcoations while holding obj->mm.lock are permissible. For the latter they are not. And get/put_pages transitions between the two types of objects. This is still not entirely fool-proof since the rules might chance. But as long as we run such a code ever at runtime lockdep should be able to observe the inconsistency and complain (like with any other lockdep class that we've split up in multiple classes). But there are a few clear benefits: - We can drop the nesting flag parameter from __i915_gem_object_put_pages, because that function by definition is never going allocate memory, and calling it on an object which doesn't have its pages allocated would be a bug. - We strictly catch more bugs, since there's not only one place in the entire tree which is annotated with the special class. All the other places that had explicit lockdep nesting annotations we're now going to leave up to lockdep again. - Specifically this catches stuff like calling get_pages from put_pages (which isn't really a good idea, if we can call put_pages so could the shrinker). I've seen patches do exactly that. Of course I fully expect CI will show me for the fool I am with this one here :-) v2: There can only be one (lockdep only has a cache for the first subclass, not for deeper ones, and we don't want to make these locks even slower). Still separate enums for better documentation. Real fix: don forget about phys objs and pin_map(), and fix the shrinker to have the right annotations ... silly me. Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> --- drivers/gpu/drm/i915/gem/i915_gem_object.c | 2 +- drivers/gpu/drm/i915/gem/i915_gem_object.h | 16 +++++++++++++--- drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 10 +++++++++- drivers/gpu/drm/i915/gem/i915_gem_pages.c | 9 ++++----- drivers/gpu/drm/i915/gem/i915_gem_phys.c | 2 +- drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 5 ++--- drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 2 +- drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 12 ++++++------ 8 files changed, 37 insertions(+), 21 deletions(-)