conn: fix Receive blocking Send#291
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In mdlayher#265, Receive was changed from RLock to Lock to serialize concurrent Receive calls. Since Send uses RLock, it blocks for as long as Receive holds the exclusive lock. When Receive is blocking in recvmsg waiting for kernel data, Send is blocked too. This causes a deadlock in patterns like NFQUEUE, where one can goroutine read packets while another sends verdicts concurrently. Fix by introducing a separate receiveMu that serializes concurrent Receive calls without holding mu exclusively, keeping Send and Receive concurrency compatible. Fixes: mdlayher#288
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@florianl Do you mind having a look ? |
florianl
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May 6, 2026
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How about a test like https://gist.github.com/florianl/13bedaf2bb26bb3c0a0ce52df9e229fb that does not depend on time.Sleep()?
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In #265, Receive was changed from RLock to Lock to serialize concurrent Receive calls. Since Send uses RLock, it blocks for as long as Receive holds the exclusive lock. When Receive is blocking in recvmsg waiting for kernel data, Send is blocked too. This causes a deadlock in patterns like NFQUEUE, where one can goroutine read packets while another sends verdicts concurrently.
Fix by introducing a separate receiveMu that serializes concurrent Receive calls without holding mu exclusively, keeping Send and Receive concurrency compatible.
Fixes: #288