| Message ID | 20190814192434.11678-1-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | RFC: drm/i915: Switch obj->mm.lock lockdep annotations on its head | expand |
> -----Original Message----- > From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On Behalf > Of Daniel Vetter > Sent: Wednesday, August 14, 2019 12:25 PM > To: Intel Graphics Development <intel-gfx@lists.freedesktop.org> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>; Vetter, Daniel > <daniel.vetter@intel.com> > Subject: [Intel-gfx] [PATCH] RFC: drm/i915: Switch obj->mm.lock lockdep > annotations on its head > > 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. > > v3: Forgot usertptr too ... I eventually looked this patch. My question is on the shrinking calling stack: Pin_pages(A)-->get_page(A)-->lock(objA->mm.lock, I915_MM_GET_PAGES)-->i915_gem_shrink()--> Lock(struct_mutex)-->put_pages(B)-->lock(objB->mm.lock).... objA is locked with: mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES); objB is locked with: mutex_lock(&obj->mm.lock); My understanding is that objB locking is equivalently to: mutex_lock_nested(&obj->mm.lock, I915_MM_NORMAL); so you lock subclass=2 first on A, then lock subclass=0 next B, the reverse order. Doesn't this cause a lockdep warning? --CQ > > 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 | 4 ++-- > drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 12 ++++++------ > 8 files changed, 38 insertions(+), 22 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c > b/drivers/gpu/drm/i915/gem/i915_gem_object.c > index 3929c3a6b281..a1a835539e09 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c > @@ -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); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h > b/drivers/gpu/drm/i915/gem/i915_gem_object.h > index 3714cf234d64..5ce511ca7fa8 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h > @@ -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); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > index d474c6ac4100..1ea3c3c96a5a 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > @@ -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; > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c > b/drivers/gpu/drm/i915/gem/i915_gem_pages.c > index 18f0ce0135c1..202526e8910f 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c > @@ -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); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > index 102fd7a23d3d..209925be8a76 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > @@ -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; > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > index edd21d14e64f..0b0d6e27b996 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > @@ -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; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > index 70dc506a5426..f3b3bc7c32cb 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > @@ -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; > @@ -514,7 +514,7 @@ __i915_gem_userptr_get_pages_worker(struct > work_struct *_work) > } > } > > - mutex_lock(&obj->mm.lock); > + mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES); > if (obj->userptr.work == &work->work) { > struct sg_table *pages = ERR_PTR(ret); > > diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > index 6cbd4a668c9a..df586035c33e 100644 > --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > @@ -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); > } > > -- > 2.22.0 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
On Thu, Aug 15, 2019 at 9:35 PM Tang, CQ <cq.tang@intel.com> wrote: > > > > > -----Original Message----- > > From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On Behalf > > Of Daniel Vetter > > Sent: Wednesday, August 14, 2019 12:25 PM > > To: Intel Graphics Development <intel-gfx@lists.freedesktop.org> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>; Vetter, Daniel > > <daniel.vetter@intel.com> > > Subject: [Intel-gfx] [PATCH] RFC: drm/i915: Switch obj->mm.lock lockdep > > annotations on its head > > > > 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. > > > > v3: Forgot usertptr too ... > > I eventually looked this patch. My question is on the shrinking calling stack: > > Pin_pages(A)-->get_page(A)-->lock(objA->mm.lock, I915_MM_GET_PAGES)-->i915_gem_shrink()--> > Lock(struct_mutex)-->put_pages(B)-->lock(objB->mm.lock).... > > objA is locked with: mutex_lock_interruptible_nested(&obj->mm.lock, I915_MM_GET_PAGES); > > objB is locked with: mutex_lock(&obj->mm.lock); > My understanding is that objB locking is equivalently to: > mutex_lock_nested(&obj->mm.lock, I915_MM_NORMAL); > > so you lock subclass=2 first on A, then lock subclass=0 next B, the reverse order. > Doesn't this cause a lockdep warning? So mutex_lock_nested really is misnamed, it should be called mutex_lock_subclass. There's no guarantees/promises about a certain nesting, just that lockdep should use the 1st/2nd/... subclass of the lockdep class the lock uses (there's a limit of 8 total, including the main/default subclass). From lockdep's pov a subclass works exactly like allocating a new lockdep key. But with the difference that you can change it at runtime, i.e. when an object makes a state transition, you can change the subclass you're using. Like this patch tries to do here. But ofc like everytime you're creating a new lockdep class, you need to spend a few words on why it's not hiding real issues from lockdep. -Daniel > --CQ > > > > > > 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 | 4 ++-- > > drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 12 ++++++------ > > 8 files changed, 38 insertions(+), 22 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c > > b/drivers/gpu/drm/i915/gem/i915_gem_object.c > > index 3929c3a6b281..a1a835539e09 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c > > @@ -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); > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h > > b/drivers/gpu/drm/i915/gem/i915_gem_object.h > > index 3714cf234d64..5ce511ca7fa8 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h > > @@ -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); > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > > b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > > index d474c6ac4100..1ea3c3c96a5a 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h > > @@ -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; > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c > > b/drivers/gpu/drm/i915/gem/i915_gem_pages.c > > index 18f0ce0135c1..202526e8910f 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c > > @@ -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); > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > index 102fd7a23d3d..209925be8a76 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > @@ -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; > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > > b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > > index edd21d14e64f..0b0d6e27b996 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c > > @@ -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; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > > b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > > index 70dc506a5426..f3b3bc7c32cb 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c > > @@ -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; > > @@ -514,7 +514,7 @@ __i915_gem_userptr_get_pages_worker(struct > > work_struct *_work) > > } > > } > > > > - mutex_lock(&obj->mm.lock); > > + mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES); > > if (obj->userptr.work == &work->work) { > > struct sg_table *pages = ERR_PTR(ret); > > > > diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > > b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > > index 6cbd4a668c9a..df586035c33e 100644 > > --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > > +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c > > @@ -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); > > } > > > > -- > > 2.22.0 > > > > _______________________________________________ > > Intel-gfx mailing list > > Intel-gfx@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c index 3929c3a6b281..a1a835539e09 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -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); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h index 3714cf234d64..5ce511ca7fa8 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h @@ -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); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h index d474c6ac4100..1ea3c3c96a5a 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h @@ -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; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c index 18f0ce0135c1..202526e8910f 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c @@ -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); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c b/drivers/gpu/drm/i915/gem/i915_gem_phys.c index 102fd7a23d3d..209925be8a76 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c @@ -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; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c index edd21d14e64f..0b0d6e27b996 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c @@ -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; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c index 70dc506a5426..f3b3bc7c32cb 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c @@ -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; @@ -514,7 +514,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work) } } - mutex_lock(&obj->mm.lock); + mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES); if (obj->userptr.work == &work->work) { struct sg_table *pages = ERR_PTR(ret); diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c index 6cbd4a668c9a..df586035c33e 100644 --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c @@ -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. v3: Forgot usertptr too ... 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 | 4 ++-- drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 12 ++++++------ 8 files changed, 38 insertions(+), 22 deletions(-)