[PATCH] dma-buf: fix debugfs versus rcu and fence dumping

[jglisse at redhat.com]

From: Jérôme Glisse <jglisse at redhat.com>

The debugfs take reference on fence without dropping them. Also the
rcu section are not well balance. Fix all that ...

Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
Cc: Christian König <christian.koenig at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Sumit Semwal <sumit.semwal at linaro.org>
Cc: linux-media at vger.kernel.org
Cc: dri-devel at lists.freedesktop.org
Cc: linaro-mm-sig at lists.linaro.org
Cc: Stéphane Marchesin <marcheu at chromium.org>
Cc: stable at vger.kernel.org
---
 drivers/dma-buf/dma-buf.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 13884474d158..f6f4de42ac49 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1051,24 +1051,31 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 			fobj = rcu_dereference(robj->fence);
 			shared_count = fobj ? fobj->shared_count : 0;
 			fence = rcu_dereference(robj->fence_excl);
+			fence = dma_fence_get_rcu(fence);
 			if (!read_seqcount_retry(&robj->seq, seq))
 				break;
 			rcu_read_unlock();
 		}
-
-		if (fence)
+		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");
+			dma_fence_put(fence);
+		}
+
+		rcu_read_lock();
 		for (i = 0; i < shared_count; i++) {
 			fence = rcu_dereference(fobj->shared[i]);
 			if (!dma_fence_get_rcu(fence))
 				continue;
+			rcu_read_unlock();
 			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
 				   fence->ops->get_driver_name(fence),
 				   fence->ops->get_timeline_name(fence),
 				   dma_fence_is_signaled(fence) ? "" : "un");
+			dma_fence_put(fence);
+			rcu_read_lock();
 		}
 		rcu_read_unlock();
 
-- 
2.17.2