Abstract the complexity of iterating over all the fences in a dma_resv object.
The new loop handles the whole RCU and retry dance and returns only fences where we can be sure we grabbed the right one.
v2: fix accessing the shared fences while they might be freed, improve kerneldoc, rename _cursor to _iter, add dma_resv_iter_is_exclusive, add dma_resv_iter_begin/end
Signed-off-by: Christian König christian.koenig@amd.com --- drivers/dma-buf/dma-resv.c | 61 +++++++++++++++++++++++++++ include/linux/dma-resv.h | 84 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 145 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 84fbe60629e3..3e77cad2c9d4 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -323,6 +323,67 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence) } EXPORT_SYMBOL(dma_resv_add_excl_fence);
+/** + * dma_resv_iter_walk_unlocked - walk over fences in a dma_resv obj + * @cursor: cursor to record the current position + * @first: if we should start over + * + * Return all the fences in the dma_resv object which are not yet signaled. + * The returned fence has an extra local reference so will stay alive. + * If a concurrent modify is detected the whole iterration is started over again. + */ +struct dma_fence *dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor, + bool first) +{ + struct dma_resv *obj = cursor->obj; + + first |= read_seqcount_retry(&obj->seq, cursor->seq); + do { + /* Drop the reference from the previous round */ + dma_fence_put(cursor->fence); + + cursor->is_first = first; + if (first) { + cursor->seq = read_seqcount_begin(&obj->seq); + cursor->index = -1; + cursor->fences = dma_resv_shared_list(obj); + + cursor->fence = dma_resv_excl_fence(obj); + if (cursor->fence && + test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, + &cursor->fence->flags)) + cursor->fence = NULL; + } else { + cursor->fence = NULL; + } + + if (cursor->fence) { + cursor->fence = dma_fence_get_rcu(cursor->fence); + } else if (cursor->all_fences && cursor->fences) { + struct dma_resv_list *fences = cursor->fences; + + while (++cursor->index < fences->shared_count) { + cursor->fence = rcu_dereference( + fences->shared[cursor->index]); + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, + &cursor->fence->flags)) + break; + } + if (cursor->index < fences->shared_count) + cursor->fence = + dma_fence_get_rcu(cursor->fence); + else + cursor->fence = NULL; + } + + /* For the eventually next round */ + first = true; + } while (read_seqcount_retry(&obj->seq, cursor->seq)); + + return cursor->fence; +} +EXPORT_SYMBOL_GPL(dma_resv_iter_walk_unlocked); + /** * dma_resv_copy_fences - Copy all fences from src to dst. * @dst: the destination reservation object diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index 9100dd3dc21f..693d16117153 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -149,6 +149,90 @@ struct dma_resv { struct dma_resv_list __rcu *fence; };
+/** + * struct dma_resv_iter - current position into the dma_resv fences + * + * Don't touch this directly in the driver, use the accessor function instead. + */ +struct dma_resv_iter { + /** @obj: The dma_resv object we iterate over */ + struct dma_resv *obj; + + /** @all_fences: If all fences should be returned */ + bool all_fences; + + /** @fence: the currently handled fence */ + struct dma_fence *fence; + + /** @seq: sequence number to check for modifications */ + unsigned int seq; + + /** @index: index into the shared fences */ + unsigned int index; + + /** @fences: the shared fences */ + struct dma_resv_list *fences; + + /** @is_first: true if this is the first returned fence */ + bool is_first; +}; + +struct dma_fence *dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor, + bool first); + +/** + * dma_resv_iter_begin - initialize a dma_resv_iter object + * @cursor: The dma_resv_iter object to initialize + * @obj: The dma_resv object which we want to iterator over + * @all_fences: If all fences should be returned or just the exclusive one + */ +static inline void dma_resv_iter_begin(struct dma_resv_iter *cursor, + struct dma_resv *obj, + bool all_fences) +{ + cursor->obj = obj; + cursor->all_fences = all_fences; + cursor->fence = NULL; +} + +/** + * dma_resv_iter_end - cleanup a dma_resv_iter object + * @cursor: the dma_resv_iter object which should be cleaned up + * + * Make sure that the reference to the fence in the cursor is properly + * dropped. + */ +static inline void dma_resv_iter_end(struct dma_resv_iter *cursor) +{ + dma_fence_put(cursor->fence); +} + +/** + * dma_resv_iter_is_exclusive - test if the current fence is the exclusive one + * @cursor: the cursor of the current position + * + * Returns true if the currently returned fence is the exclusive one. + */ +static inline bool dma_resv_iter_is_exclusive(struct dma_resv_iter *cursor) +{ + return cursor->index == -1; +} + +/** + * dma_resv_for_each_fence_unlocked - unlocked fence iterator + * @cursor: a struct dma_resv_iter pointer + * @fence: the current fence + * + * Iterate over the fences in a struct dma_resv object without holding the + * dma_resv::lock. The RCU read side lock must be hold when using this, but can + * be dropped and re-taken as necessary inside the loop. The cursor needs to be + * initialized with dma_resv_iter_begin_unlocked() and cleaned up with + * dma_resv_iter_end_unlocked(). + */ +#define dma_resv_for_each_fence_unlocked(cursor, fence) \ + for (fence = dma_resv_iter_walk_unlocked(cursor, true); \ + fence; fence = dma_resv_iter_walk_unlocked(cursor, false)) + #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base) #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)