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Commitbe4b0c0

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Avoid lockup of a parallel worker when reporting a long error message.
Because sigsetjmp() will restore the initial state with signals blocked,the code path in bgworker.c for reporting an error and exiting wouldexecute that way. Usually this is fairly harmless; but if a parallelworker had an error message exceeding the shared-memory communicationbuffer size (16K) it would lock up, because it would wait for aresume-sending signal from its parallel leader which it would neverdetect.To fix, just unblock signals at the appropriate point.This can be shown to fail back to 9.6. The lack of parallel queryinfrastructure makes it difficult to provide a simple test case for9.5; but I'm pretty sure the issue exists in some form there as well,so apply the code change there too.Vignesh C, reviewed by Bharath Rupireddy, Robert Haas, and myselfDiscussion:https://postgr.es/m/CALDaNm1d1hHPZUg3xU4XjtWBOLCrA+-2cJcLpw-cePZ=GgDVfA@mail.gmail.com
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‎src/backend/postmaster/bgworker.c

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -743,7 +743,7 @@ StartBackgroundWorker(void)
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/*
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* If an exception is encountered, processing resumes here.
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*
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*See notes in postgres.c aboutthedesign of this coding.
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*We just need to clean up, reporttheerror, and go away.
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*/
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if (sigsetjmp(local_sigjmp_buf,1)!=0)
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{
@@ -753,7 +753,14 @@ StartBackgroundWorker(void)
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/* Prevent interrupts while cleaning up */
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HOLD_INTERRUPTS();
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/* Report the error to the server log */
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/*
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* sigsetjmp will have blocked all signals, but we may need to accept
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* signals while communicating with our parallel leader. Once we've
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* done HOLD_INTERRUPTS() it should be safe to unblock signals.
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*/
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BackgroundWorkerUnblockSignals();
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/* Report the error to the parallel leader and the server log */
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EmitErrorReport();
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/*

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