Commit 885660bd authored by Michael Roth's avatar Michael Roth Committed by Anthony Liguori
Browse files

network scripts: don't block SIGCHLD before forking 



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:

7c3370d4

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:

4d54ec78

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

Reviewed-by: default avatarJan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent f603a687

net/tap.c

+0 −6
Original line number Diff line number Diff line
@@ -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;