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Re: [Qemu-devel] [PATCH v3] network scripts: don't block SIGCHLD before

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v3] network scripts: don't block SIGCHLD before forking
Date: Mon, 12 Dec 2011 09:01:47 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20110930 Thunderbird/7.0.1

On 12/08/2011 04:48 AM, Michael Roth wrote:
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


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:


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 |    6 ------
  1 files changed, 0 insertions(+), 6 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index 1f26dc9..6c27a94 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -346,15 +346,10 @@ static TAPState *net_tap_fd_init(VLANState *vlan,

  static int launch_script(const char *setup_script, const char *ifname, int fd)
-    sigset_t oldmask, mask;
      int pid, status;
      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 +373,6 @@ 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;

Reviewed-by: Paolo Bonzini <address@hidden>


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