Move extra code out of the Pre/PostRestoreCommand() section.

If SIGTERM is received within this section, the startup process
will immediately proc_exit() in the signal handler, so it is
inadvisable to include any more code than is required there (as
such code is unlikely to be compatible with doing proc_exit() in a
signal handler).  This commit moves the code recently added to this
section (see 1b06d7bac9 and 7fed801135) to outside of the section.
This ensures that the startup process only calls proc_exit() in its
SIGTERM handler for the duration of the system() call, which is how
this code worked from v8.4 to v14.

Reported-by: Michael Paquier, Thomas Munro
Analyzed-by: Andres Freund
Suggested-by: Tom Lane
Reviewed-by: Michael Paquier, Robert Haas, Thomas Munro, Andres Freund
Discussion: https://postgr.es/m/Y9nGDSgIm83FHcad%40paquier.xyz
Discussion: https://postgr.es/m/20230223231503.GA743455%40nathanxps13
Backpatch-through: 15

diff --git a/src/backend/access/transam/xlogarchive.c b/src/backend/access/transam/xlogarchive.c
index f3fb92c8f96f97450eea849d714b3119ead290d2..524e80adb1ccd4e4b6d6251a3e0f23ce66daa95e 100644 (file)
--- a/src/backend/access/transam/xlogarchive.c
+++ b/src/backend/access/transam/xlogarchive.c
@@ -159,20 +159,27 @@ RestoreArchivedFile(char *path, const char *xlogfname,
                        (errmsg_internal("executing restore command \"%s\"",
                                                         xlogRestoreCmd)));
 
+       fflush(NULL);
+       pgstat_report_wait_start(WAIT_EVENT_RESTORE_COMMAND);
+
        /*
-        * Check signals before restore command and reset afterwards.
+        * PreRestoreCommand() informs the SIGTERM handler for the startup process
+        * that it should proc_exit() right away.  This is done for the duration
+        * of the system() call because there isn't a good way to break out while
+        * it is executing.  Since we might call proc_exit() in a signal handler,
+        * it is best to put any additional logic before or after the
+        * PreRestoreCommand()/PostRestoreCommand() section.
         */
        PreRestoreCommand();
 
        /*
         * Copy xlog from archival storage to XLOGDIR
         */
-       fflush(NULL);
-       pgstat_report_wait_start(WAIT_EVENT_RESTORE_COMMAND);
        rc = system(xlogRestoreCmd);
-       pgstat_report_wait_end();
 
        PostRestoreCommand();
+
+       pgstat_report_wait_end();
        pfree(xlogRestoreCmd);
 
        if (rc == 0)