[Qemu-devel] [PATCH v2] network scripts: don't block SIGCHLD before forking

[Michael Roth]

This patch fixes a bug where child processes of launch_script() can
misbehave due to SIGCHLD being blocked. In the case of `sudo`, this
causes a permanent hang.

Previously a SIGCHLD handler was added to reap fork_exec()'d zombie
processes by calling waitpid(-1, ...). This required other
fork()/waitpid() callers to temporarilly block SIGCHILD to avoid
having the final wait status being intercepted by the SIGCHLD
handler:

7c3370d4fe3fa6cda8655f109e4659afc8ca4269

Since then, the qemu_add_child_watch() interface was added to allow
registration of such processes and reap only from that specific set
of PIDs:

4d54ec7898bd951007cb6122d5315584bd41d0c4

As a result, we can now avoid blocking SIGCHLD in launch_script(), so
drop that behavior.

Signed-off-by: Michael Roth <address@hidden>
---
 net/tap.c |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index 1f26dc9..2cf79e1 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -351,10 +351,6 @@ static int launch_script(const char *setup_script, const 
char *ifname, int fd)
     char *args[3];
     char **parg;
 
-    sigemptyset(&mask);
-    sigaddset(&mask, SIGCHLD);
-    sigprocmask(SIG_BLOCK, &mask, &oldmask);
-
     /* try to launch network script */
     pid = fork();
     if (pid == 0) {
@@ -378,7 +374,6 @@ static int launch_script(const char *setup_script, const 
char *ifname, int fd)
         while (waitpid(pid, &status, 0) != pid) {
             /* loop */
         }
-        sigprocmask(SIG_SETMASK, &oldmask, NULL);
 
         if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
             return 0;
-- 
1.7.4.1