Fix segmentation fault that commit ac22929a26 caused.

Commit ac22929a26 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
index e081bf926089215c713dd7c93979fbc35dde68e3..a1078a7cfcab071fb113f399f0d8f6b013d9de8e 100644 (file)
--- 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);
 }
 
 /*