Fix assertion failure when updating full_page_writes for checkpointer.

When the checkpointer receives a SIGHUP signal to update its configuration,
it may need to update the shared memory for full_page_writes and need to
write a WAL record for it.  Now, it is quite possible that the XLOG
machinery has not been initialized by that time and it will lead to
assertion failure while doing that.  Fix is to allow the initialization of
the XLOG machinery outside critical section.

This bug has been introduced by the commit 2c03216d83 which added the XLOG
machinery initialization in RecoveryInProgress code path.

Reported-by: Dilip Kumar
Author: Dilip Kumar
Reviewed-by: Michael Paquier and Amit Kapila
Backpatch-through: 9.5
Discussion: https://postgr.es/m/CAFiTN-u4BA8KXcQUWDPNgaKAjDXC=C2whnzBM8TAcv=stckYUw@mail.gmail.com

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 5abaeb005b38dff4e4704e5167e20cbaf92c3364..7375a78ffcfb7cbab73b69ddf985c19a3f67c36c 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9701,6 +9701,7 @@ void
 UpdateFullPageWrites(void)
 {
        XLogCtlInsert *Insert = &XLogCtl->Insert;
+       bool            recoveryInProgress;
 
        /*
         * Do nothing if full_page_writes has not been changed.
@@ -9712,6 +9713,13 @@ UpdateFullPageWrites(void)
        if (fullPageWrites == Insert->fullPageWrites)
                return;
 
+       /*
+        * Perform this outside critical section so that the WAL insert
+        * initialization done by RecoveryInProgress() doesn't trigger an
+        * assertion failure.
+        */
+       recoveryInProgress = RecoveryInProgress();
+
        START_CRIT_SECTION();
 
        /*
@@ -9732,7 +9740,7 @@ UpdateFullPageWrites(void)
         * Write an XLOG_FPW_CHANGE record. This allows us to keep track of
         * full_page_writes during archive recovery, if required.
         */
-       if (XLogStandbyInfoActive() && !RecoveryInProgress())
+       if (XLogStandbyInfoActive() && !recoveryInProgress)
        {
                XLogBeginInsert();
                XLogRegisterData((char *) (&fullPageWrites), sizeof(bool));