From 63efab4ca139ab18095b8e095d5708d5566fc9e2 Mon Sep 17 00:00:00 2001
From: Thomas Munro <tmunro@postgresql.org>
Date: Tue, 18 Sep 2018 22:56:36 +1200
Subject: [PATCH] Allow DSM allocation to be interrupted.
Chris Travers reported that the startup process can repeatedly try to
cancel a backend that is in a posix_fallocate()/EINTR loop and cause it
to loop forever. Teach the retry loop to give up if an interrupt is
pending. 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 later
back-patched).
Author: Chris Travers
Reviewed-by: Ildar Musin, Murat Kabilov, Oleksii Kliukin
Tested-by: Oleksii Kliukin
Discussion: https://postgr.es/m/CAN-RpxB-oeZve_J3SM_6%3DHXPmvEG%3DHX%2B9V9pi8g2YR7YW0rBBg%40mail.gmail.com
---
src/backend/storage/ipc/dsm_impl.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index c6382ec031b..b79701d8375 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -47,6 +47,7 @@
*/
#include "postgres.h"
+#include "miscadmin.h"
#include <fcntl.h>
#include <unistd.h>
@@ -333,6 +334,14 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
shm_unlink(name);
errno = save_errno;
+ /*
+ * If we received a query cancel or termination signal, we will have
+ * EINTR set here. If the caller said that errors are OK here, check
+ * for interrupts immediately.
+ */
+ if (errno == EINTR && elevel >= ERROR)
+ CHECK_FOR_INTERRUPTS();
+
ereport(elevel,
(errcode_for_dynamic_shared_memory(),
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)
#if defined(HAVE_POSIX_FALLOCATE) && defined(__linux__)
if (rc == 0)
{
- /* We may get interrupted, if so just retry. */
+ /*
+ * We may get interrupted. If so, just retry unless there is an
+ * interrupt pending. This avoids the possibility of looping forever
+ * if another backend is repeatedly trying to interrupt us.
+ */
do
{
rc = posix_fallocate(fd, 0, size);
- } while (rc == EINTR);
+ } while (rc == EINTR && !(ProcDiePending || QueryCancelPending));
/*
* The caller expects errno to be set, but posix_fallocate() doesn't
--
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