[PATCH 1/7] dma-buf: fix inconsistent debug print

[Christian König]

The code tries to acquire the rcu protected fence list, but then ignores
individual fences which have 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 eadd1eaa2fb5..d3b4e370dbc1 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