Make dsm_impl_posix_resize more future-proof.

Commit 4518c798 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 a65e0864
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 4518c798 and 80845b7c.

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
index 4419c4b465e9339c0c76f17a83646e7a764db34c..c51e3e683c92a26eb433702edc095a075a5b3074 100644 (file)
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -49,6 +49,7 @@
 #include "postgres.h"
 
 #include <fcntl.h>
+#include <signal.h>
 #include <unistd.h>
 #ifndef WIN32
 #include <sys/mman.h>
@@ -62,7 +63,7 @@
 #endif
 
 #include "common/file_perm.h"
-#include "libpq/pqsignal.h"        /* for PG_SETMASK macro */
+#include "libpq/pqsignal.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "portability/mem.h"
@@ -355,6 +356,7 @@ 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
@@ -363,7 +365,7 @@ 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
@@ -406,7 +408,7 @@ 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;
    }