Patchwork [v3] network scripts: don't block SIGCHLD before forking

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Submitter Michael Roth
Date Dec. 8, 2011, 3:48 a.m.
Message ID <1323316087-1070-1-git-send-email-mdroth@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/130090/
State New
Headers show

Comments

Michael Roth - Dec. 8, 2011, 3:48 a.m.
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 <mdroth@linux.vnet.ibm.com>
---
 net/tap.c |    6 ------
 1 files changed, 0 insertions(+), 6 deletions(-)
Jan Kiszka - Dec. 8, 2011, 1:36 p.m.
On 2011-12-08 04:48, 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
> 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 <mdroth@linux.vnet.ibm.com>
> ---
>  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;

Looks sane.

Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Paolo Bonzini - Dec. 12, 2011, 8:01 a.m.
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
> 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<mdroth@linux.vnet.ibm.com>
> ---
>   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 <pbonzini@redhat.com>

Paolo
Anthony Liguori - Dec. 15, 2011, 6:09 p.m.
On 12/07/2011 09:48 PM, 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
> 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<mdroth@linux.vnet.ibm.com>

Applied.  Thanks.

Regards,

Anthony Liguori

> ---
>   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;

Patch

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;