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authorChristian Krinitsin <mail@krinitsin.com>2025-07-17 09:10:43 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-07-17 09:10:43 +0200
commitf2ec263023649e596c5076df32c2d328bc9393d2 (patch)
tree5dd86caab46e552bd2e62bf9c4fb1a7504a44db4 /results/scraper/fex/4131
parent63d2e9d409831aa8582787234cae4741847504b7 (diff)
downloadqemu-analysis-main.tar.gz
qemu-analysis-main.zip
add downloaded fex bug-reports HEAD main
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+Bear's Restaurant has race condition with deferred signal handling
+[Bear's Restaurant](https://store.steampowered.com/app/1687550/Bears_Restaurant/) has a race condition with FEX's deferred signal handling. Its [game engine](https://ebitengine.org/) is based on golang, which sends SIGURG /very/ quickly for doing preemption to ensure thread fairness.

+

+A couple of things to fix in FEX's deferred signal handling.

+- If its not a realtime signal, then these shouldn't be queued and instead just set in a mask of available signals.

+  - Linux doesn't queue non-RT signals, expecting many non-RT signals to be lost rather than queued

+- FEX should block the `sa_mask` in the signal handler of the signal getting deferred, to ensure it doesn't receive anymore of that signal.

+  - This would ensure FEX doesn't overrun its small signal queue, which can typically result in crashes.

+  - Make sure to restore signal mask once actually handling the signal

+

+I don't have time to implement these fixes right now but I needed a tracking issue to remember it.

+

+I originally wanted to test this engine to see it break under Asahi Linux, but apparently it uses a new enough version of golang that it no longer hits the VDSO bug, might need to try an older game using this engine to see the Asahi breakage.
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