[glibc] nptl: Reorder semaphore release in tst-cancel7

[Maciej W. Rozycki]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=934ba77add195dde2c922b4ae809968cde62a1ff

commit 934ba77add195dde2c922b4ae809968cde62a1ff
Author: Maciej W. Rozycki <macro@redhat.com>
Date:   Wed Aug 7 19:46:21 2024 +0100

    nptl: Reorder semaphore release in tst-cancel7
    
    Move the release of the semaphore used to synchronize between an extra
    copy of the test run as a separate process and the main test process
    until after the PID file has been locked.  It is so that if the cleanup
    function gets called by the test driver due to premature termination of
    the main test process, then the function does not get at the PID file
    before it has been locked and conclude that the extra copy of the test
    has already terminated.  This won't usually happen due to a relatively
    high amount of time required to elapse before timeout triggers in the
    test driver, but it will change with the next change.
    
    There is still a small time window remaining with this change in place
    where the main test process gets killed for some reason between the
    extra copy of the test has been already started by pthread_create(3) and
    a successful return from the call to sem_wait(3), in which case the
    cleanup function can be reached before PID has been written to the PID
    file and the file locked.  It seems that with the test case structured
    as it is now and PID-based process management we have no means to avoid
    it.
    
    Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Diff:
---
 nptl/tst-cancel7.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/nptl/tst-cancel7.c b/nptl/tst-cancel7.c
index d2350bde20..574429098c 100644
--- a/nptl/tst-cancel7.c
+++ b/nptl/tst-cancel7.c
@@ -57,9 +57,6 @@ sl (void)
   fprintf (f, "%lld\n", (long long) getpid ());
   fflush (f);
 
-  if (sem_post (sem) != 0)
-    FAIL_EXIT1 ("sem_post: %m");
-
   struct flock fl =
     {
       .l_type = F_WRLCK,
@@ -70,6 +67,9 @@ sl (void)
   if (fcntl (fileno (f), F_SETLK, &fl) != 0)
     FAIL_EXIT1 ("fcntl (F_SETFL): %m");
 
+  if (sem_post (sem) != 0)
+    FAIL_EXIT1 ("sem_post: %m");
+
   sigset_t ss;
   sigfillset (&ss);
   sigsuspend (&ss);
@@ -116,7 +116,7 @@ do_test (void)
 {
   pthread_t th = xpthread_create (NULL, tf, NULL);
 
-  /* Wait to cancel until after the pid is written.  */
+  /* Wait to cancel until after the pid is written and file locked.  */
   if (sem_wait (sem) != 0)
     FAIL_EXIT1 ("sem_wait: %m");