Fix segmentation fault that commit ac22929 caused.

MasaoFujii · MasaoFujii · commit 113d3591b859 · 2020-11-04T21:49:00.000+09:00
Commit ac22929 changed recoveryWakeupLatch so that it's reset to NULL at the end of recovery. This change could cause a segmentation fault in the buildfarm member 'elver'. Previously the latch was reset to NULL after calling ShutdownWalRcv(). But there could be a window between ShutdownWalRcv() and the actual exit of walreceiver. If walreceiver set the latch during that window, the segmentation fault could happen. To fix the issue, this commit changes walreceiver so that it sets the latch only when the latch has not been reset to NULL yet. Author: Fujii Masao Discussion: https://postgr.es/m/5c1f8a85-747c-7bf9-241e-dd467d8a3586@iki.fi
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -12673,7 +12673,8 @@ CheckPromoteSignal(void)
 void
 WakeupRecovery(void)
 {
-	SetLatch(XLogCtl->recoveryWakeupLatch);
+	if (XLogCtl->recoveryWakeupLatch)
+		SetLatch(XLogCtl->recoveryWakeupLatch);
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -12673,7 +12673,8 @@ CheckPromoteSignal(void)`
`12673`	`12673`	`void`
`12674`	`12674`	`WakeupRecovery(void)`
`12675`	`12675`	`{`
`12676`		`- SetLatch(XLogCtl->recoveryWakeupLatch);`
	`12676`	`+ if (XLogCtl->recoveryWakeupLatch)`
	`12677`	`+ SetLatch(XLogCtl->recoveryWakeupLatch);`
`12677`	`12678`	`}`
`12678`	`12679`
`12679`	`12680`	`/*`