Re: [LTP] [PATCH] Synchronization between two processes

[Subrata Modak <subrata@linux.vnet.ibm.com>]

On Fri, 2009-05-22 at 13:55 +0800, Wei Yongjun wrote: 
> Serge E. Hallyn wrote:
> > Quoting Subrata Modak (subrata@linux.vnet.ibm.com):
> >   
> >> On Fri, 2009-05-15 at 08:45 -0500, Serge E. Hallyn wrote: 
> >>     
> >>> Quoting Gui Xiaohua (guixh@cn.fujitsu.com):
> >>>       
> >>>> The child-process wait SIGUSR1 which would be sended by parent-process,
> >>>> if the child-process execute sigtimedwait() after parent-process send 
> >>>> the signal, it would never receive the SIGUSR1 from parent-process.
> >>>> I cann't make sure the SIGUSR1 be sended after child-process execute 
> >>>> sigtimedwait() with 100 percent, and i try my best.
> >>>>         
> >>> Well, in theory I suppose this could happen, but you'd have to have
> >>> a pretty bad scheduler if the parent can do a strcmp(buf, "c:go")
> >>> between the pipe read and signal send, while the child goes straight
> >>> from pipe write to sigtimedwait.
> >>>
> >>> Have you seen this signal be missed?  If not, then I'd rather assume
> >>> things are reasonable.  If you have seen this happen, then why not
> >>> instead set up a SIGUSR1 handler in the child before doing the pipe
> >>> write, then just sleep for 3 seconds instead of doing sigtimedwait?
> >>>       
> >> Thanks Serge.
> >>     
> >
> > Or, if I'm being unreasonable, then at least have the parent only wait
> > for at most 1 second, and leave the child alone.  Every every ltp test
> > is going to hang for 5 seconds...
> >
> > But I prefer setting the signal handler ahead of time.
> >
> >   
> Sorry to relpy late.
> 
> As your last advice, i change the test case, and it work will.
> 
> [PATCH] fix sync problem between two processes of pidns12 test
> 
> The child-process wait SIGUSR1 which would be sended by parent-process,
> if the child-process execute sigtimedwait() after parent-process send
> the signal, it would never receive the SIGUSR1 from parent-process.
> 
> This patch rewrite child_signal_handler() to handle to SIGUSR1 and
> instead sigtimedwait() with sleep for 3 seconds.
> 
> Signed-off-by: Gui Xiaohua <guixh@cn.fujitsu.com>

Serge,

Your view on this new solution ?

Regards--
Subrata

> ---
>  testcases/kernel/containers/pidns/pidns12.c |   35 ++++++--------------------
>  1 files changed, 8 insertions(+), 27 deletions(-)
> 
> diff --git a/testcases/kernel/containers/pidns/pidns12.c b/testcases/kernel/containers/pidns/pidns12.c
> index f893021..9120e82 100644
> --- a/testcases/kernel/containers/pidns/pidns12.c
> +++ b/testcases/kernel/containers/pidns/pidns12.c
> @@ -72,8 +72,13 @@ void cleanup()
>   */
>  static void child_signal_handler(int sig, siginfo_t *si, void *unused)
>  {
> -	/* sigtimedwait() traps siginfo details, so this wont be called */
> -	tst_resm(TWARN, "cinit: control should have not reached here!");
> +	/* Recieved SIGUSR1. Check sender pid */
> +	if (si->si_pid == 0)
> +		tst_resm(TPASS, "cinit: signalling PID (from other namespace)"\
> +				" is 0 as expected");
> +	else
> +		tst_resm(TFAIL, "cinit: signalling PID (from other namespace)"\
> +				" is not 0, but %d.", si->si_pid);
>  }
> 
>  /*
> @@ -82,9 +87,6 @@ static void child_signal_handler(int sig, siginfo_t *si, void *unused)
>  int child_fn(void *arg)
>  {
>  	struct sigaction sa;
> -	sigset_t newset;
> -	siginfo_t info;
> -	struct timespec timeout;
>  	pid_t pid, ppid;
> 
>  	/* Set process id and parent pid */
> @@ -108,34 +110,13 @@ int child_fn(void *arg)
>  		cleanup();
>  	}
> 
> -	/* Set timeout for sigtimedwait */
> -	timeout.tv_sec = 3;
> -	timeout.tv_nsec = 0;
> -
> -	/* Set mask to wait for SIGUSR1 signal */
> -	sigemptyset(&newset);
> -	sigaddset(&newset, SIGUSR1);
> -
>  	/* Let parent to signal SIGUSR1 */
>  	if (write(pipefd[1], "c:go\0", 5) != 5) {
>  		tst_resm(TBROK, "cinit: pipe is broken to write");
>  		cleanup();
>  	}
> 
> -	/* Wait for SIGUSR1 */
> -	if (sigtimedwait(&newset, &info, &timeout) != SIGUSR1) {
> -		tst_resm(TBROK, "cinit: sigtimedwait() failed(%s).",
> -				strerror(errno));
> -		cleanup();
> -	}
> -
> -	/* Recieved SIGUSR1. Check sender pid */
> -	if (info.si_pid == 0)
> -		tst_resm(TPASS, "cinit: signalling PID (from other namespace)"\
> -				" is 0 as expected");
> -	else
> -		tst_resm(TFAIL, "cinit: signalling PID (from other namespace)"\
> -				" is not 0, but %d.", info.si_pid);
> +	sleep(3);
> 
>  	/* cleanup and exit */
>  	close(pipefd[1]);


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