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Alexander found a interesting case: 1. We have a queue of two waiters in a blocked_queue 2. first file descriptor changes state to RUNNABLE, second changes to INVALID 3. awaitEvent function dequeued RUNNABLE thread to a run queue and attempted to dequeue INVALID descriptor to a run queue. Unqueueing INVALID fails thusly: #3 0x000000000045cf1c in barf (s=0x4c1cb0 "removeThreadFromDeQueue: not found") at rts/RtsMessages.c:42 #4 0x000000000046848b in removeThreadFromDeQueue (...) at rts/Threads.c:249 #5 0x000000000049a120 in removeFromQueues (...) at rts/RaiseAsync.c:719 #6 0x0000000000499502 in throwToSingleThreaded__ (...) at rts/RaiseAsync.c:67 #7 0x0000000000499555 in throwToSingleThreaded (..) at rts/RaiseAsync.c:75 #8 0x000000000047c27d in awaitEvent (wait=rtsFalse) at rts/posix/Select.c:415 The problem here is a throwToSingleThreaded function that tries to unqueue a TSO from blocked_queue, but awaitEvent function leaves blocked_queue in a inconsistent state while traverses over blocked_queue: case RTS_FD_IS_READY: IF_DEBUG(scheduler, debugBelch("Waking up blocked thread %lu\n", (unsigned long)tso->id)); tso->why_blocked = NotBlocked; tso->_link = END_TSO_QUEUE; // Here we break the queue head pushOnRunQueue(&MainCapability,tso); break; Signed-off-by: Sergei Trofimovich <siarheit@google.com> Test Plan: tested on a sample from T10590 Reviewers: austin, bgamari, simonmar Reviewed By: bgamari, simonmar Subscribers: qnikst, thomie, bgamari Differential Revision: https://phabricator.haskell.org/D1024 GHC Trac Issues: #10590, #4934
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