Hmm, just looking at what kind of locking we have in place for accessing the state of an apzc I found this https://searchfox.org/mozilla-central/rev/c59d9181cbcd8356ce9271723e31be11641e7010/gfx/layers/apz/src/AsyncPanZoomController.h#1277 "This is in theory protected by |mRecursiveMutex|; that is, it should be held whenever this is updated. In practice though... see bug 897017." And there is also bug 1153979. So I'm not sure if there is just one place we need to hold the mutex but don't or there are already systematic problems in many other places we are aware of by haven't tackled yet.
Bug 1685837 Comment 1 Edit History
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Hmm, just looking at what kind of locking we have in place for accessing the state of an apzc I found this https://searchfox.org/mozilla-central/rev/c59d9181cbcd8356ce9271723e31be11641e7010/gfx/layers/apz/src/AsyncPanZoomController.h#1277 "This is in theory protected by |mRecursiveMutex|; that is, it should be held whenever this is updated. In practice though... see bug 897017." And there is also bug 1153979. So I'm not sure if there is just one place we need to hold the mutex but don't or there are already systematic problems in many other places we are aware of but haven't tackled yet.