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

[Wei Yongjun <yjwei@cn.fujitsu.com>]

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>
---
 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]);
-- 
1.6.3




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