On 22/09/2021 10:10, Christian König wrote:
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
v3: restructor the code, move rcu_read_lock()/unlock() into the iterator, add dma_resv_iter_is_restarted()
v4: fix NULL deref when no explicit fence exists, drop superflous rcu_read_lock()/unlock() calls.
Signed-off-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-resv.c | 95 ++++++++++++++++++++++++++++++++++++++ include/linux/dma-resv.h | 95 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 190 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 84fbe60629e3..7768140ab36d 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -323,6 +323,101 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence) } EXPORT_SYMBOL(dma_resv_add_excl_fence); +/**
- dma_resv_iter_restart_unlocked - restart the unlocked iterator
- @cursor: The dma_resv_iter object to restart
- Restart the unlocked iteration by initializing the cursor object.
- */
+static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor) +{
- cursor->seq = read_seqcount_begin(&cursor->obj->seq);
- cursor->index = -1;
- if (cursor->all_fences)
cursor->fences = dma_resv_shared_list(cursor->obj);
- else
cursor->fences = NULL;
- cursor->is_restarted = true;
+}
+/**
- dma_resv_iter_walk_unlocked - walk over fences in a dma_resv obj
- @cursor: cursor to record the current position
- 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.
iteration
- */
+static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) +{
- struct dma_resv *obj = cursor->obj;
- do {
/* Drop the reference from the previous round */
dma_fence_put(cursor->fence);
if (cursor->index++ == -1) {
cursor->fence = dma_resv_excl_fence(obj);
} else if (!cursor->fences ||
cursor->index >= cursor->fences->shared_count) {
cursor->fence = NULL;
} else {
struct dma_resv_list *fences = cursor->fences;
unsigned int idx = cursor->index;
cursor->fence = rcu_dereference(fences->shared[idx]);
}
if (cursor->fence)
cursor->fence = dma_fence_get_rcu(cursor->fence);
- } while (cursor->fence && dma_fence_is_signaled(cursor->fence));
+}
+/**
- dma_resv_iter_first_unlocked - first fence in an unlocked dma_resv obj.
- @cursor: the cursor with the current position
- Returns the first fence from an unlocked dma_resv obj.
- */
+struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor) +{
- rcu_read_lock();
- do {
dma_resv_iter_restart_unlocked(cursor);
dma_resv_iter_walk_unlocked(cursor);
- } while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));
- rcu_read_unlock();
- return cursor->fence;
+} +EXPORT_SYMBOL(dma_resv_iter_first_unlocked);
Why is this one split from dma_resv_iter_begin and even exported? I couldn't find any users in the series.
+/**
- dma_resv_iter_next_unlocked - next fence in an unlocked dma_resv obj.
- @cursor: the cursor with the current position
- Returns the next fence from an unlocked dma_resv obj.
- */
+struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor) +{
- bool restart;
- rcu_read_lock();
- cursor->is_restarted = false;
- restart = read_seqcount_retry(&cursor->obj->seq, cursor->seq);
- do {
if (restart)
dma_resv_iter_restart_unlocked(cursor);
dma_resv_iter_walk_unlocked(cursor);
restart = true;
- } while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));
- rcu_read_unlock();
- return cursor->fence;
+} +EXPORT_SYMBOL(dma_resv_iter_next_unlocked);
Couldn't dma_resv_iter_first_unlocked and dma_resv_iter_next_unlocked share the same implementation? Especially if you are able to replace cursor->is_restarted with cursor->index == -1.
- /**
- 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..baf77a542392 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -149,6 +149,101 @@ 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_restarted: true if this is the first returned fence */
- bool is_restarted;
+};
+struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor); +struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor);
+/**
- 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
iterate
- @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_iter_is_restarted - test if this is the first fence after a restart
- @cursor: the cursor with the current position
- Return true if this is the first fence in an interation after a restart.
iteration
- */
+static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor) +{
- return cursor->is_restarted;
+}
+/**
- 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 and using RCU instead. The cursor needs to be initialized
- with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside
- the iterator a reference to the dma_fence is hold and the RCU lock dropped.
held
- When the dma_resv is modified the iteration starts over again.
- */
+#define dma_resv_for_each_fence_unlocked(cursor, fence) \
- for (fence = dma_resv_iter_first_unlocked(cursor); \
fence; fence = dma_resv_iter_next_unlocked(cursor))
- #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base) #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
Regards,
Tvrtko