From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 1 Feb 2014 21:21:04 +0000 (-0500)
Subject: Fix some more bugs in signal handlers and process shutdown logic.
X-Git-Tag: REL9_2_7~30
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=81b116d987a779de7c97f5fd415a7c8348b9afff;p=postgresql

Fix some more bugs in signal handlers and process shutdown logic.

WalSndKill was doing things exactly backwards: it should first clear
MyWalSnd (to stop signal handlers from touching MyWalSnd->latch),
then disown the latch, and only then mark the WalSnd struct unused by
clearing its pid field.

Also, WalRcvSigUsr1Handler and worker_spi_sighup failed to preserve
errno, which is surely a requirement for any signal handler.

Per discussion of recent buildfarm failures.  Back-patch as far
as the relevant code exists.
---

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index bd64c2873f..fdf44a46e5 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -950,17 +950,23 @@ InitWalSnd(void)
 static void
 WalSndKill(int code, Datum arg)
 {
-	Assert(MyWalSnd != NULL);
+	WalSnd	   *walsnd = MyWalSnd;
+
+	Assert(walsnd != NULL);
+
+	/*
+	 * Clear MyWalSnd first; then disown the latch.  This is so that signal
+	 * handlers won't try to touch the latch after it's no longer ours.
+	 */
+	MyWalSnd = NULL;
+
+	DisownLatch(&walsnd->latch);
 
 	/*
 	 * Mark WalSnd struct no longer in use. Assume that no lock is required
 	 * for this.
 	 */
-	MyWalSnd->pid = 0;
-	DisownLatch(&MyWalSnd->latch);
-
-	/* WalSnd struct isn't mine anymore */
-	MyWalSnd = NULL;
+	walsnd->pid = 0;
 }
 
 /*