reservation: add suppport for read-only access using rcu
This adds some extra functions to deal with rcu.
reservation_object_get_fences_rcu() will obtain the list of shared
and exclusive fences without obtaining the ww_mutex.
reservation_object_wait_timeout_rcu() will wait on all fences of the
reservation_object, without obtaining the ww_mutex.
reservation_object_test_signaled_rcu() will test if all fences of the
reservation_object are signaled without using the ww_mutex.
reservation_object_get_excl and reservation_object_get_list require
the reservation object to be held, updating requires
write_seqcount_begin/end. If only the exclusive fence is needed,
rcu_dereference followed by fence_get_rcu can be used, if the shared
fences are needed it's recommended to use the supplied functions.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-By: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index cb8379d..f3014c4 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -137,7 +137,7 @@
struct reservation_object_list *fobj;
struct fence *fence_excl;
unsigned long events;
- unsigned shared_count;
+ unsigned shared_count, seq;
dmabuf = file->private_data;
if (!dmabuf || !dmabuf->resv)
@@ -151,14 +151,20 @@
if (!events)
return 0;
- ww_mutex_lock(&resv->lock, NULL);
+retry:
+ seq = read_seqcount_begin(&resv->seq);
+ rcu_read_lock();
- fobj = resv->fence;
- if (!fobj)
- goto out;
-
- shared_count = fobj->shared_count;
- fence_excl = resv->fence_excl;
+ fobj = rcu_dereference(resv->fence);
+ if (fobj)
+ shared_count = fobj->shared_count;
+ else
+ shared_count = 0;
+ fence_excl = rcu_dereference(resv->fence_excl);
+ if (read_seqcount_retry(&resv->seq, seq)) {
+ rcu_read_unlock();
+ goto retry;
+ }
if (fence_excl && (!(events & POLLOUT) || shared_count == 0)) {
struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
@@ -176,14 +182,20 @@
spin_unlock_irq(&dmabuf->poll.lock);
if (events & pevents) {
- if (!fence_add_callback(fence_excl, &dcb->cb,
+ if (!fence_get_rcu(fence_excl)) {
+ /* force a recheck */
+ events &= ~pevents;
+ dma_buf_poll_cb(NULL, &dcb->cb);
+ } else if (!fence_add_callback(fence_excl, &dcb->cb,
dma_buf_poll_cb)) {
events &= ~pevents;
+ fence_put(fence_excl);
} else {
/*
* No callback queued, wake up any additional
* waiters.
*/
+ fence_put(fence_excl);
dma_buf_poll_cb(NULL, &dcb->cb);
}
}
@@ -205,13 +217,26 @@
goto out;
for (i = 0; i < shared_count; ++i) {
- struct fence *fence = fobj->shared[i];
+ struct fence *fence = rcu_dereference(fobj->shared[i]);
+ if (!fence_get_rcu(fence)) {
+ /*
+ * fence refcount dropped to zero, this means
+ * that fobj has been freed
+ *
+ * call dma_buf_poll_cb and force a recheck!
+ */
+ events &= ~POLLOUT;
+ dma_buf_poll_cb(NULL, &dcb->cb);
+ break;
+ }
if (!fence_add_callback(fence, &dcb->cb,
dma_buf_poll_cb)) {
+ fence_put(fence);
events &= ~POLLOUT;
break;
}
+ fence_put(fence);
}
/* No callback queued, wake up any additional waiters. */
@@ -220,7 +245,7 @@
}
out:
- ww_mutex_unlock(&resv->lock);
+ rcu_read_unlock();
return events;
}