Restore SIGCHLD to SIG_DFL where we care about waitpid().

It was reported that under one implementation of socks client
"git clone" fails with "error: waitpid failed (No child processes)",
because "git" is spawned after setting SIGCHLD to SIG_IGN.

Arguably it may be a broken setting, but we should protect
ourselves so that we can get reliable results from waitpid() for
the children we care about.

This patch resets SIGCHLD to SIG_DFL in three places:

 - connect.c::git_connect() - initiators of git native
   protocol transfer are covered with this.

 - daemon.c::main() - obviously.

 - merge-index.c::main() - obviously.

There are other programs that do fork() but do not waitpid():
http-push, imap-send.  upload-pack does not either, but in the
case of that program, each of the forked halves runs exec()
another program, so this change would not have much effect
there.

Signed-off-by: Junio C Hamano <junkio@cox.net>

3 files changed, 15 insertions, 0 deletions

diff --git a/connect.c b/connect.c
index 52d709e58d..db7342e4d2 100644
--- a/connect.c
+++ b/connect.c
@@ -581,6 +581,11 @@ int git_connect(int fd[2], char *url, const char *prog)
 	enum protocol protocol = PROTO_LOCAL;
 	int free_path = 0;
 
+	/* Without this we cannot rely on waitpid() to tell
+	 * what happened to our children.
+	 */
+	signal(SIGCHLD, SIG_DFL);
+
 	host = strstr(url, "://");
 	if(host) {
 		*host = '\0';
diff --git a/daemon.c b/daemon.c
index 2f03f99d2d..10670047f2 100644
--- a/daemon.c
+++ b/daemon.c
@@ -671,6 +671,11 @@ int main(int argc, char **argv)
 	int inetd_mode = 0;
 	int i;
 
+	/* Without this we cannot rely on waitpid() to tell
+	 * what happened to our children.
+	 */
+	signal(SIGCHLD, SIG_DFL);
+
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];
 
diff --git a/merge-index.c b/merge-index.c
index 024196e7ac..190e12fb7c 100644
--- a/merge-index.c
+++ b/merge-index.c
@@ -99,6 +99,11 @@ int main(int argc, char **argv)
 {
 	int i, force_file = 0;
 
+	/* Without this we cannot rely on waitpid() to tell
+	 * what happened to our children.
+	 */
+	signal(SIGCHLD, SIG_DFL);
+
 	if (argc < 3)
 		usage("git-merge-index [-o] [-q] <merge-program> (-a | <filename>*)");