From 419113dfdc4c729f6c763cc30a9b02ee68a7da94 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 20 Sep 2016 12:04:41 -0400
Subject: [PATCH] Retry DSM control segment creation if Windows indicates
access denied.
Otherwise, attempts to run multiple postmasters running on the same
machine may fail, because Windows sometimes returns ERROR_ACCESS_DENIED
rather than ERROR_ALREADY_EXISTS when there is an existing segment.
Hitting this bug is much more likely because of another defect not
fixed by this patch, namely that dsm_postmaster_startup() uses
random() which returns the same value every time. But that's not
a reason not to fix this.
Kyotaro Horiguchi and Amit Kapila, reviewed by Michael Paquier
Discussion: <CAA4eK1JyNdMeF-dgrpHozDecpDfsRZUtpCi+1AbtuEkfG3YooQ@mail.gmail.com>
---
src/backend/storage/ipc/dsm_impl.c | 31 +++++++++++++++++-------------
1 file changed, 18 insertions(+), 13 deletions(-)
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 99051f02c8c..7122c4abe00 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -671,6 +671,7 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
{
DWORD size_high;
DWORD size_low;
+ DWORD errcode;
/* Shifts >= the width of the type are undefined. */
#ifdef _WIN64
@@ -686,27 +687,31 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
size_high, /* Upper 32 bits of size */
size_low, /* Lower 32 bits of size */
name);
+
+ errcode = GetLastError();
+ if (errcode == ERROR_ALREADY_EXISTS || errcode == ERROR_ACCESS_DENIED)
+ {
+ /*
+ * On Windows, when the segment already exists, a handle for the
+ * existing segment is returned. We must close it before
+ * returning. However, if the existing segment is created by a
+ * service, then it returns ERROR_ACCESS_DENIED. We don't do
+ * _dosmaperr here, so errno won't be modified.
+ */
+ if (hmap)
+ CloseHandle(hmap);
+ return false;
+ }
+
if (!hmap)
{
- _dosmaperr(GetLastError());
+ _dosmaperr(errcode);
ereport(elevel,
(errcode_for_dynamic_shared_memory(),
errmsg("could not create shared memory segment \"%s\": %m",
name)));
return false;
}
- _dosmaperr(GetLastError());
- if (errno == EEXIST)
- {
- /*
- * On Windows, when the segment already exists, a handle for the
- * existing segment is returned. We must close it before
- * returning. We don't do _dosmaperr here, so errno won't be
- * modified.
- */
- CloseHandle(hmap);
- return false;
- }
}
else
{
--
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