[PATCH 01/11] dma-buf: fix invalid debug print

[Christian König]

The code tries to acquire the rcu protected fence list, but then ignores
individual fences which has been modified while holding the rcu.

Stop that madness and just note cleanly that
the list was concurrently modified.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/dma-buf.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index f264b70c383e..468c282b8a06 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1383,22 +1383,17 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 				buf_obj->name ?: "");
 
 		robj = buf_obj->resv;
-		while (true) {
-			seq = read_seqcount_begin(&robj->seq);
-			rcu_read_lock();
-			fobj = rcu_dereference(robj->fence);
-			shared_count = fobj ? fobj->shared_count : 0;
-			fence = rcu_dereference(robj->fence_excl);
-			if (!read_seqcount_retry(&robj->seq, seq))
-				break;
-			rcu_read_unlock();
-		}
-
+		seq = read_seqcount_begin(&robj->seq);
+		rcu_read_lock();
+		fence = rcu_dereference(robj->fence_excl);
 		if (fence)
 			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
 				   fence->ops->get_driver_name(fence),
 				   fence->ops->get_timeline_name(fence),
 				   dma_fence_is_signaled(fence) ? "" : "un");
+
+		fobj = rcu_dereference(robj->fence);
+		shared_count = fobj ? fobj->shared_count : 0;
 		for (i = 0; i < shared_count; i++) {
 			fence = rcu_dereference(fobj->shared[i]);
 			if (!dma_fence_get_rcu(fence))
@@ -1410,6 +1405,8 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 			dma_fence_put(fence);
 		}
 		rcu_read_unlock();
+		if (read_seqcount_retry(&robj->seq, seq))
+			seq_printf(s, "\tFences concurrently modified\n");
 
 		seq_puts(s, "\tAttached Devices:\n");
 		attach_count = 0;
-- 
2.25.1