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UDP poll/select currently reports POLLIN as soon as UDP_NEWDATA is seen in the callback path. At that point the datagram may not yet be queued into conn->readahead, so a waiter can wake up before recvfrom() has consumable data.\n\nDefer the UDP POLLIN notification in udp_poll_eventhandler() and notify poll/select waiters only after udp_datahandler() has queued the datagram into read-ahead. This keeps poll/select readiness aligned with what recvfrom() can actually read.\n\nThis issue was observed on a loopback UDP control socket where select() woke early and recv() returned before the reply was buffered.
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masc2008
marked this pull request as draft
August 25, 2026 02:06
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@masc2008 please fix the Summary, seems like your modification corrupted it: 
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Summary\n- defer UDP readiness until the datagram has been queued into \n- keep and existing immediate readahead checks unchanged\n- align / readiness with what can actually consume\n\n## Problem\n currently raises as soon as is seen in the callback path. However, the datagram is only queued into UDP read-ahead later in via . That allows a waiter to wake up before has consumable data buffered.\n\n## Fix\nThis change removes the early notification from and notifies UDP poll/select waiters only after has queued the datagram into .\n\n## Validation\nThis was validated on a downstream NuttX-based target by tracing the UDP callback path and confirming the ordering changed from:\n\n- poll/select wake\n- queue into read-ahead\n\nto:\n\n- queue into read-ahead\n- poll/select wake\n\nwhich eliminated an observed early-wakeup race on a loopback UDP control socket.