[LEDE-DEV] [PATCH libubox 1/2] uloop: Fix race condition in SIGCHLD handling

[Yousong Zhou]

On 12 September 2017 at 19:12, Michal Sojka <sojkam1 at fel.cvut.cz> wrote:
> When uloop_process_add() is called outside of uloop_run(), i.e. not
> from a callback (which is the case of at least utrace and ujail),
> child events can be missed. The reason is that when SIGCHILD handler
> is installed in uloop_run(), after the uloop_process_add() is called,
> then an initial signal could be missed.
>
> Commit 4e3a47a ("uloop: use a waker for notifying sigchld and loop
> cancel events", 2016-06-09) solved a similar problem and introduced
> uloop_init() but forgot to move a call to uloop_setup_signals() there.
> This is what this commit does.
>
> Now, uloop_process_add() can be called any time after uloop_init()
> without missing any event.
>
> Signed-off-by: Michal Sojka <sojkam1 at fel.cvut.cz>

Acked-by: Yousong Zhou <yszhou4tech at gmail.com>

Thanks.
                yousong

> ---
>  uloop.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/uloop.c b/uloop.c
> index d2f41bb..3813e18 100644
> --- a/uloop.c
> +++ b/uloop.c
> @@ -116,6 +116,8 @@ static int waker_init(void)
>         return 0;
>  }
>
> +static void uloop_setup_signals(bool add);
> +
>  int uloop_init(void)
>  {
>         if (uloop_init_pollfd() < 0)
> @@ -126,6 +128,8 @@ int uloop_init(void)
>                 return -1;
>         }
>
> +       uloop_setup_signals(true);
> +
>         return 0;
>  }
>
> @@ -525,12 +529,7 @@ int uloop_run_timeout(int timeout)
>         int next_time = 0;
>         struct timeval tv;
>
> -       /*
> -        * Handlers are only updated for the first call to uloop_run() (and restored
> -        * when this call is done).
> -        */
> -       if (!uloop_run_depth++)
> -               uloop_setup_signals(true);
> +       uloop_run_depth++;
>
>         uloop_status = 0;
>         uloop_cancelled = false;
> @@ -553,14 +552,15 @@ int uloop_run_timeout(int timeout)
>                 uloop_run_events(next_time);
>         }
>
> -       if (!--uloop_run_depth)
> -               uloop_setup_signals(false);
> +       --uloop_run_depth;
>
>         return uloop_status;
>  }
>
>  void uloop_done(void)
>  {
> +       uloop_setup_signals(false);
> +
>         if (poll_fd >= 0) {
>                 close(poll_fd);
>                 poll_fd = -1;
> --
> 2.14.1
>
>
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