This helper existed to handle the weird corner-cases caused by using SLAB_TYPESAFE_BY_RCU for backing dma_fence. Now that no one is using that anymore (i915 was the only real user), dma_fence_get_rcu is sufficient. The one slightly annoying thing we have to deal with here is that dma_fence_get_rcu_safe did an rcu_dereference as well as a SLAB_TYPESAFE_BY_RCU-safe dma_fence_get_rcu. This means each call site ends up being 3 lines instead of 1.
Signed-off-by: Jason Ekstrand jason@jlekstrand.net Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Christian König christian.koenig@amd.com Cc: Matthew Auld matthew.auld@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com --- drivers/dma-buf/dma-fence-chain.c | 8 ++-- drivers/dma-buf/dma-resv.c | 4 +- drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 4 +- drivers/gpu/drm/i915/i915_active.h | 4 +- drivers/gpu/drm/i915/i915_vma.c | 4 +- include/drm/drm_syncobj.h | 4 +- include/linux/dma-fence.h | 50 ----------------------- include/linux/dma-resv.h | 4 +- 8 files changed, 23 insertions(+), 59 deletions(-)
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c index 7d129e68ac701..46dfc7d94d8ed 100644 --- a/drivers/dma-buf/dma-fence-chain.c +++ b/drivers/dma-buf/dma-fence-chain.c @@ -15,15 +15,17 @@ static bool dma_fence_chain_enable_signaling(struct dma_fence *fence); * dma_fence_chain_get_prev - use RCU to get a reference to the previous fence * @chain: chain node to get the previous node from * - * Use dma_fence_get_rcu_safe to get a reference to the previous fence of the - * chain node. + * Use rcu_dereference and dma_fence_get_rcu to get a reference to the + * previous fence of the chain node. */ static struct dma_fence *dma_fence_chain_get_prev(struct dma_fence_chain *chain) { struct dma_fence *prev;
rcu_read_lock(); - prev = dma_fence_get_rcu_safe(&chain->prev); + prev = rcu_dereference(chain->prev); + if (prev) + prev = dma_fence_get_rcu(prev); rcu_read_unlock(); return prev; } diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index f26c71747d43a..cfe0db3cca292 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -376,7 +376,9 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) dst_list = NULL; }
- new = dma_fence_get_rcu_safe(&src->fence_excl); + new = rcu_dereference(src->fence_excl); + if (new) + new = dma_fence_get_rcu(new); rcu_read_unlock();
src_list = dma_resv_shared_list(dst); diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c index 72d9b92b17547..0aeb6117f3893 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c @@ -161,7 +161,9 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f, struct dma_fence *old;
rcu_read_lock(); - old = dma_fence_get_rcu_safe(ptr); + old = rcu_dereference(*ptr); + if (old) + old = dma_fence_get_rcu(old); rcu_read_unlock();
if (old) { diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h index d0feda68b874f..bd89cfc806ca5 100644 --- a/drivers/gpu/drm/i915/i915_active.h +++ b/drivers/gpu/drm/i915/i915_active.h @@ -103,7 +103,9 @@ i915_active_fence_get(struct i915_active_fence *active) struct dma_fence *fence;
rcu_read_lock(); - fence = dma_fence_get_rcu_safe(&active->fence); + fence = rcu_dereference(active->fence); + if (fence) + fence = dma_fence_get_rcu(fence); rcu_read_unlock();
return fence; diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c index 0f227f28b2802..ed0388d99197e 100644 --- a/drivers/gpu/drm/i915/i915_vma.c +++ b/drivers/gpu/drm/i915/i915_vma.c @@ -351,7 +351,9 @@ int i915_vma_wait_for_bind(struct i915_vma *vma) struct dma_fence *fence;
rcu_read_lock(); - fence = dma_fence_get_rcu_safe(&vma->active.excl.fence); + fence = rcu_dereference(vma->active.excl.fence); + if (fence) + fence = dma_fence_get_rcu(fence); rcu_read_unlock(); if (fence) { err = dma_fence_wait(fence, MAX_SCHEDULE_TIMEOUT); diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h index 6cf7243a1dc5e..6c45d52988bcc 100644 --- a/include/drm/drm_syncobj.h +++ b/include/drm/drm_syncobj.h @@ -105,7 +105,9 @@ drm_syncobj_fence_get(struct drm_syncobj *syncobj) struct dma_fence *fence;
rcu_read_lock(); - fence = dma_fence_get_rcu_safe(&syncobj->fence); + fence = rcu_dereference(syncobj->fence); + if (fence) + fence = dma_fence_get_rcu(syncobj->fence); rcu_read_unlock();
return fence; diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 6ffb4b2c63715..f4a2ab2b1ae46 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -307,56 +307,6 @@ static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence) return NULL; }
-/** - * dma_fence_get_rcu_safe - acquire a reference to an RCU tracked fence - * @fencep: pointer to fence to increase refcount of - * - * Function returns NULL if no refcount could be obtained, or the fence. - * This function handles acquiring a reference to a fence that may be - * reallocated within the RCU grace period (such as with SLAB_TYPESAFE_BY_RCU), - * so long as the caller is using RCU on the pointer to the fence. - * - * An alternative mechanism is to employ a seqlock to protect a bunch of - * fences, such as used by struct dma_resv. When using a seqlock, - * the seqlock must be taken before and checked after a reference to the - * fence is acquired (as shown here). - * - * The caller is required to hold the RCU read lock. - */ -static inline struct dma_fence * -dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep) -{ - do { - struct dma_fence *fence; - - fence = rcu_dereference(*fencep); - if (!fence) - return NULL; - - if (!dma_fence_get_rcu(fence)) - continue; - - /* The atomic_inc_not_zero() inside dma_fence_get_rcu() - * provides a full memory barrier upon success (such as now). - * This is paired with the write barrier from assigning - * to the __rcu protected fence pointer so that if that - * pointer still matches the current fence, we know we - * have successfully acquire a reference to it. If it no - * longer matches, we are holding a reference to some other - * reallocated pointer. This is possible if the allocator - * is using a freelist like SLAB_TYPESAFE_BY_RCU where the - * fence remains valid for the RCU grace period, but it - * may be reallocated. When using such allocators, we are - * responsible for ensuring the reference we get is to - * the right fence, as below. - */ - if (fence == rcu_access_pointer(*fencep)) - return rcu_pointer_handoff(fence); - - dma_fence_put(fence); - } while (1); -} - #ifdef CONFIG_LOCKDEP bool dma_fence_begin_signalling(void); void dma_fence_end_signalling(bool cookie); diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index 562b885cf9c3d..a38c021f379af 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -248,7 +248,9 @@ dma_resv_get_excl_unlocked(struct dma_resv *obj) return NULL;
rcu_read_lock(); - fence = dma_fence_get_rcu_safe(&obj->fence_excl); + fence = rcu_dereference(obj->fence_excl); + if (fence) + fence = dma_fence_get_rcu(fence); rcu_read_unlock();
return fence;