2 files changed, 55 insertions, 4 deletions

diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 138bdec47e9..1972aecbedc 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -247,14 +247,17 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 	/*
 	 * Create new segment or open an existing one for attach.
 	 *
-	 * Even though we're not going through fd.c, we should be safe against
-	 * running out of file descriptors, because of NUM_RESERVED_FDS.  We're
-	 * only opening one extra descriptor here, and we'll close it before
-	 * returning.
+	 * Even though we will close the FD before returning, it seems desirable
+	 * to use Reserve/ReleaseExternalFD, to reduce the probability of EMFILE
+	 * failure.  The fact that we won't hold the FD open long justifies using
+	 * ReserveExternalFD rather than AcquireExternalFD, though.
 	 */
+	ReserveExternalFD();
+
 	flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
 	if ((fd = shm_open(name, flags, PG_FILE_MODE_OWNER)) == -1)
 	{
+		ReleaseExternalFD();
 		if (errno != EEXIST)
 			ereport(elevel,
 					(errcode_for_dynamic_shared_memory(),
@@ -278,6 +281,7 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 			/* Back out what's already been done. */
 			save_errno = errno;
 			close(fd);
+			ReleaseExternalFD();
 			errno = save_errno;
 
 			ereport(elevel,
@@ -295,6 +299,7 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 		/* Back out what's already been done. */
 		save_errno = errno;
 		close(fd);
+		ReleaseExternalFD();
 		shm_unlink(name);
 		errno = save_errno;
 
@@ -323,6 +328,7 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 		/* Back out what's already been done. */
 		save_errno = errno;
 		close(fd);
+		ReleaseExternalFD();
 		if (op == DSM_OP_CREATE)
 			shm_unlink(name);
 		errno = save_errno;
@@ -336,6 +342,7 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
 	*mapped_address = address;
 	*mapped_size = request_size;
 	close(fd);
+	ReleaseExternalFD();
 
 	return true;
 }
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index cbd495225ca..046ca5c6c7e 100644
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -51,6 +51,7 @@
 #include "port/atomics.h"
 #include "portability/instr_time.h"
 #include "postmaster/postmaster.h"
+#include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
 #include "storage/pmsignal.h"
@@ -187,6 +188,9 @@ InitializeLatchSupport(void)
 			/* Clean up, just for safety's sake; we'll set these below */
 			selfpipe_readfd = selfpipe_writefd = -1;
 			selfpipe_owner_pid = 0;
+			/* Keep fd.c's accounting straight */
+			ReleaseExternalFD();
+			ReleaseExternalFD();
 		}
 		else
 		{
@@ -194,6 +198,7 @@ InitializeLatchSupport(void)
 			 * Postmaster didn't create a self-pipe ... or else we're in an
 			 * EXEC_BACKEND build, in which case it doesn't matter since the
 			 * postmaster's pipe FDs were closed by the action of FD_CLOEXEC.
+			 * fd.c won't have state to clean up, either.
 			 */
 			Assert(selfpipe_readfd == -1);
 		}
@@ -228,6 +233,10 @@ InitializeLatchSupport(void)
 	selfpipe_readfd = pipefd[0];
 	selfpipe_writefd = pipefd[1];
 	selfpipe_owner_pid = MyProcPid;
+
+	/* Tell fd.c about these two long-lived FDs */
+	ReserveExternalFD();
+	ReserveExternalFD();
 #else
 	/* currently, nothing to do here for Windows */
 #endif
@@ -604,24 +613,57 @@ CreateWaitEventSet(MemoryContext context, int nevents)
 	set->exit_on_postmaster_death = false;
 
 #if defined(WAIT_USE_EPOLL)
+	if (!AcquireExternalFD())
+	{
+		/* treat this as though epoll_create1 itself returned EMFILE */
+		elog(ERROR, "epoll_create1 failed: %m");
+	}
 #ifdef EPOLL_CLOEXEC
 	set->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
 	if (set->epoll_fd < 0)
+	{
+		ReleaseExternalFD();
 		elog(ERROR, "epoll_create1 failed: %m");
+	}
 #else
 	/* cope with ancient glibc lacking epoll_create1 (e.g., RHEL5) */
 	set->epoll_fd = epoll_create(nevents);
 	if (set->epoll_fd < 0)
+	{
+		ReleaseExternalFD();
 		elog(ERROR, "epoll_create failed: %m");
+	}
 	if (fcntl(set->epoll_fd, F_SETFD, FD_CLOEXEC) == -1)
+	{
+		int			save_errno = errno;
+
+		close(set->epoll_fd);
+		ReleaseExternalFD();
+		errno = save_errno;
 		elog(ERROR, "fcntl(F_SETFD) failed on epoll descriptor: %m");
+	}
 #endif							/* EPOLL_CLOEXEC */
 #elif defined(WAIT_USE_KQUEUE)
+	if (!AcquireExternalFD())
+	{
+		/* treat this as though kqueue itself returned EMFILE */
+		elog(ERROR, "kqueue failed: %m");
+	}
 	set->kqueue_fd = kqueue();
 	if (set->kqueue_fd < 0)
+	{
+		ReleaseExternalFD();
 		elog(ERROR, "kqueue failed: %m");
+	}
 	if (fcntl(set->kqueue_fd, F_SETFD, FD_CLOEXEC) == -1)
+	{
+		int			save_errno = errno;
+
+		close(set->kqueue_fd);
+		ReleaseExternalFD();
+		errno = save_errno;
 		elog(ERROR, "fcntl(F_SETFD) failed on kqueue descriptor: %m");
+	}
 	set->report_postmaster_not_running = false;
 #elif defined(WAIT_USE_WIN32)
 
@@ -655,8 +697,10 @@ FreeWaitEventSet(WaitEventSet *set)
 {
 #if defined(WAIT_USE_EPOLL)
 	close(set->epoll_fd);
+	ReleaseExternalFD();
 #elif defined(WAIT_USE_KQUEUE)
 	close(set->kqueue_fd);
+	ReleaseExternalFD();
 #elif defined(WAIT_USE_WIN32)
 	WaitEvent  *cur_event;