[libcamera-devel,v2,1/3] gstreamer: Fix deadlock when last allocator ref is held by buffer
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Message ID 20210826132346.1238420-2-nicolas@ndufresne.ca
State Accepted
Commit 1ca5513396b4fa52f7305e19b7db0ae525dbd730
Headers show
Series
  • Fix Gnome Cheese and multiple camera
Related show

Commit Message

Nicolas Dufresne Aug. 26, 2021, 1:23 p.m. UTC 
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>

This deadlock occurs when a buffer is holding the last reference on
the allocator. In gst_libcamera_allocator_release() we must drop the
object lock before dropping the last ref of that object since the
destructor will lock it again causing deadlock.

This was notice while switching camera or resolution in Cheese software.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 src/gstreamer/gstlibcameraallocator.cpp | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

Patch
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diff --git a/src/gstreamer/gstlibcameraallocator.cpp b/src/gstreamer/gstlibcameraallocator.cpp
index 7bd8ba2d..a8fa4f86 100644
--- a/src/gstreamer/gstlibcameraallocator.cpp
+++ b/src/gstreamer/gstlibcameraallocator.cpp
@@ -108,15 +108,18 @@  gst_libcamera_allocator_release(GstMiniObject *mini_object)
 {
 	GstMemory *mem = GST_MEMORY_CAST(mini_object);
 	GstLibcameraAllocator *self = GST_LIBCAMERA_ALLOCATOR(mem->allocator);
-	GLibLocker lock(GST_OBJECT(self));
-	auto *frame = reinterpret_cast<FrameWrap *>(gst_mini_object_get_qdata(mini_object, FrameWrap::getQuark()));
 
-	gst_memory_ref(mem);
+	{
+		GLibLocker lock(GST_OBJECT(self));
+		auto *frame = reinterpret_cast<FrameWrap *>(gst_mini_object_get_qdata(mini_object, FrameWrap::getQuark()));
+
+		gst_memory_ref(mem);
 
-	if (frame->releasePlane()) {
-		auto *pool = reinterpret_cast<GQueue *>(g_hash_table_lookup(self->pools, frame->stream_));
-		g_return_val_if_fail(pool, TRUE);
-		g_queue_push_tail(pool, frame);
+		if (frame->releasePlane()) {
+			auto *pool = reinterpret_cast<GQueue *>(g_hash_table_lookup(self->pools, frame->stream_));
+			g_return_val_if_fail(pool, TRUE);
+			g_queue_push_tail(pool, frame);
+		}
 	}
 
 	/* Keep last in case we are holding on the last allocator ref. */