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Commit63efab4

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Allow DSM allocation to be interrupted.
Chris Travers reported that the startup process can repeatedly try tocancel a backend that is in a posix_fallocate()/EINTR loop and cause itto loop forever. Teach the retry loop to give up if an interrupt ispending. Don't actually check for interrupts in that loop though,because a non-local exit would skip some clean-up code in the caller.Back-patch to 9.4 where DSM was added (and posix_fallocate() was laterback-patched).Author: Chris TraversReviewed-by: Ildar Musin, Murat Kabilov, Oleksii KliukinTested-by: Oleksii KliukinDiscussion:https://postgr.es/m/CAN-RpxB-oeZve_J3SM_6%3DHXPmvEG%3DHX%2B9V9pi8g2YR7YW0rBBg%40mail.gmail.com
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‎src/backend/storage/ipc/dsm_impl.c

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -47,6 +47,7 @@
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*/
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#include"postgres.h"
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#include"miscadmin.h"
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#include<fcntl.h>
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#include<unistd.h>
@@ -333,6 +334,14 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
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shm_unlink(name);
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errno=save_errno;
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/*
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* If we received a query cancel or termination signal, we will have
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* EINTR set here. If the caller said that errors are OK here, check
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* for interrupts immediately.
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*/
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if (errno==EINTR&&elevel >=ERROR)
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CHECK_FOR_INTERRUPTS();
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ereport(elevel,
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(errcode_for_dynamic_shared_memory(),
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errmsg("could not resize shared memory segment \"%s\" to %zu bytes: %m",
@@ -422,11 +431,15 @@ dsm_impl_posix_resize(int fd, off_t size)
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#if defined(HAVE_POSIX_FALLOCATE)&& defined(__linux__)
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if (rc==0)
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{
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/* We may get interrupted, if so just retry. */
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/*
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* We may get interrupted. If so, just retry unless there is an
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* interrupt pending. This avoids the possibility of looping forever
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* if another backend is repeatedly trying to interrupt us.
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*/
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do
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{
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rc=posix_fallocate(fd,0,size);
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}while (rc==EINTR);
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}while (rc==EINTR&& !(ProcDiePending||QueryCancelPending));
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/*
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* The caller expects errno to be set, but posix_fallocate() doesn't

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