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* [PATCH 2/3] lockdep: add might_lock_nested()
       [not found] <20191104173720.2696-1-daniel.vetter@ffwll.ch>
@ 2019-11-04 17:37 ` Daniel Vetter
  2019-11-04 17:37 ` [PATCH 3/3] drm/i915: use might_lock_nested in get_pages annotation Daniel Vetter
  1 sibling, 0 replies; 3+ messages in thread
From: Daniel Vetter @ 2019-11-04 17:37 UTC (permalink / raw)
  To: Intel Graphics Development
  Cc: Daniel Vetter, Peter Zijlstra, Daniel Vetter, Ingo Molnar,
	Will Deacon, linux-kernel

Necessary to annotate functions where we might acquire a
mutex_lock_nested() or similar. Needed by i915.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
 include/linux/lockdep.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index e0eca94e58c8..c4155436e6fc 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -628,6 +628,13 @@ do {									\
 	lock_acquire(&(lock)->dep_map, 0, 0, 1, 1, NULL, _THIS_IP_);	\
 	lock_release(&(lock)->dep_map, 0, _THIS_IP_);			\
 } while (0)
+# define might_lock_nested(lock, subclass) 				\
+do {									\
+	typecheck(struct lockdep_map *, &(lock)->dep_map);		\
+	lock_acquire(&(lock)->dep_map, subclass, 0, 1, 1, NULL,		\
+		     _THIS_IP_);					\
+	lock_release(&(lock)->dep_map, 0, _THIS_IP_);		\
+} while (0)
 
 #define lockdep_assert_irqs_enabled()	do {				\
 		WARN_ONCE(debug_locks && !current->lockdep_recursion &&	\
@@ -650,6 +657,7 @@ do {									\
 #else
 # define might_lock(lock) do { } while (0)
 # define might_lock_read(lock) do { } while (0)
+# define might_lock_nested(lock, subclass) do { } while (0)
 # define lockdep_assert_irqs_enabled() do { } while (0)
 # define lockdep_assert_irqs_disabled() do { } while (0)
 # define lockdep_assert_in_irq() do { } while (0)
-- 
2.24.0.rc2


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* [PATCH 3/3] drm/i915: use might_lock_nested in get_pages annotation
       [not found] <20191104173720.2696-1-daniel.vetter@ffwll.ch>
  2019-11-04 17:37 ` [PATCH 2/3] lockdep: add might_lock_nested() Daniel Vetter
@ 2019-11-04 17:37 ` Daniel Vetter
  2019-11-05  9:02   ` [Intel-gfx] " Joonas Lahtinen
  1 sibling, 1 reply; 3+ messages in thread
From: Daniel Vetter @ 2019-11-04 17:37 UTC (permalink / raw)
  To: Intel Graphics Development
  Cc: Daniel Vetter, Daniel Vetter, Peter Zijlstra, Ingo Molnar,
	Will Deacon, linux-kernel

So strictly speaking the existing annotation is also ok, because we
have a chain of

obj->mm.lock#I915_MM_GET_PAGES -> fs_reclaim -> obj->mm.lock

(the shrinker cannot get at an object while we're in get_pages, hence
this is safe). But it's confusing, so try to take the right subclass
of the lock.

This does a bit reduce our lockdep based checking, but then it's also
less fragile, in case we ever change the nesting around.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/i915/gem/i915_gem_object.h | 36 +++++++++++-----------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index edaf7126a84d..e5750d506cc9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -271,10 +271,27 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
 int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
 
+enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */
+	I915_MM_NORMAL = 0,
+	/*
+	 * 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,
+};
+
 static inline int __must_check
 i915_gem_object_pin_pages(struct drm_i915_gem_object *obj)
 {
-	might_lock(&obj->mm.lock);
+	might_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
 
 	if (atomic_inc_not_zero(&obj->mm.pages_pin_count))
 		return 0;
@@ -317,23 +334,6 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
 	__i915_gem_object_unpin_pages(obj);
 }
 
-enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */
-	I915_MM_NORMAL = 0,
-	/*
-	 * 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);
 void i915_gem_object_truncate(struct drm_i915_gem_object *obj);
 void i915_gem_object_writeback(struct drm_i915_gem_object *obj);
-- 
2.24.0.rc2


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* Re: [Intel-gfx] [PATCH 3/3] drm/i915: use might_lock_nested in get_pages annotation
  2019-11-04 17:37 ` [PATCH 3/3] drm/i915: use might_lock_nested in get_pages annotation Daniel Vetter
@ 2019-11-05  9:02   ` Joonas Lahtinen
  0 siblings, 0 replies; 3+ messages in thread
From: Joonas Lahtinen @ 2019-11-05  9:02 UTC (permalink / raw)
  To: Daniel Vetter, Intel Graphics Development
  Cc: Peter Zijlstra, Daniel Vetter, linux-kernel, Ingo Molnar,
	Daniel Vetter, Will Deacon

Quoting Daniel Vetter (2019-11-04 19:37:20)
> So strictly speaking the existing annotation is also ok, because we
> have a chain of
> 
> obj->mm.lock#I915_MM_GET_PAGES -> fs_reclaim -> obj->mm.lock
> 
> (the shrinker cannot get at an object while we're in get_pages, hence
> this is safe). But it's confusing, so try to take the right subclass
> of the lock.
> 
> This does a bit reduce our lockdep based checking, but then it's also
> less fragile, in case we ever change the nesting around.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: linux-kernel@vger.kernel.org

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas

^ permalink raw reply	[flat|nested] 3+ messages in thread

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     [not found] <20191104173720.2696-1-daniel.vetter@ffwll.ch>
2019-11-04 17:37 ` [PATCH 2/3] lockdep: add might_lock_nested() Daniel Vetter
2019-11-04 17:37 ` [PATCH 3/3] drm/i915: use might_lock_nested in get_pages annotation Daniel Vetter
2019-11-05  9:02   ` [Intel-gfx] " Joonas Lahtinen

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