Make dsm_impl_posix_resize more future-proof.

macdice · macdice · commit 1661c40b9deb · 2022-07-16T12:23:34.000+12:00
Commit 4518c79 blocks signals for a short region of code, but it assumed that whatever called it had the signal mask set to UnBlockSig on entry. That may be true today (or may even not be, in extensions in the wild), but it would be better not to make that assumption. We should save-and-restore the caller's signal mask. The PG_SETMASK() portability macro couldn't be used for that, which is why it wasn't done before. But... considering that commit a65e086 established back in 9.6 that supported POSIX systems have sigprocmask(), and that this is POSIX-only code, there is no reason not to use standard sigprocmask() directly to achieve that. Back-patch to all supported releases, like 4518c79 and 80845b7. Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CA%2BhUKGKx6Biq7_UuV0kn9DW%2B8QWcpJC1qwhizdtD9tN-fn0H0g%40mail.gmail.com
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
@@ -50,6 +50,7 @@
 #include "miscadmin.h"
 
 #include <fcntl.h>
+#include <signal.h>
 #include <unistd.h>
 #ifndef WIN32
 #include <sys/mman.h>
@@ -63,7 +64,7 @@
 #endif
 
 #include "common/file_perm.h"
-#include "libpq/pqsignal.h"		/* for PG_SETMASK macro */
+#include "libpq/pqsignal.h"
 #include "pgstat.h"
 #include "portability/mem.h"
 #include "storage/dsm_impl.h"
@@ -345,6 +346,7 @@ dsm_impl_posix_resize(int fd, off_t size)
 {
 	int			rc;
 	int			save_errno;
+	sigset_t	save_sigmask;
 
 	/*
 	 * Block all blockable signals, except SIGQUIT.  posix_fallocate() can run
@@ -353,7 +355,7 @@ dsm_impl_posix_resize(int fd, off_t size)
 	 * conflicts), the retry loop might never succeed.
 	 */
 	if (IsUnderPostmaster)
-		PG_SETMASK(&BlockSig);
+		sigprocmask(SIG_SETMASK, &BlockSig, &save_sigmask);
 
 	/* Truncate (or extend) the file to the requested size. */
 	do
@@ -394,7 +396,7 @@ dsm_impl_posix_resize(int fd, off_t size)
 	if (IsUnderPostmaster)
 	{
 		save_errno = errno;
-		PG_SETMASK(&UnBlockSig);
+		sigprocmask(SIG_SETMASK, &save_sigmask, NULL);
 		errno = save_errno;
 	}
 
