[LTP] [PATCH v1] fzsync: break inf loop with flag vs pthread_cancel

[Li Wang]

Hi Edward,

On Wed, Apr 6, 2022 at 1:06 AM Edward Liaw via ltp <ltp@lists.linux.it>
wrote:

> Hi, I'm working to get fzsync working with the Android kernel, which
> does not have pthread_cancel available.
>
> In the absence of pthread_cancel, when thread A exits due to a break,
> thread B will get stuck in an infinite loop while waiting for thread A
> to progress.
>
> Instead of cancelling thread B, we can use the exit flag to break out of
> thread B's loop.  This should also remove the need for the wrapper
> around the thread.
>


This method is more graceful, but involves a new potential issue.

Looking at tst_fzsync_run_a, if anything goes wrong in other places
(thread_b) and break with setting 'pair->exit' to 1 to end the looping.
It doesn't work for thread_a because tst_atomic_store(exit, &pair->exit)
will reset it back to 0 (int exit = 0).

Another suggestion is to distinguish the abnormal invoke for
tst_fzsync_pair_cleanup, because that is rarely a situation we
encounter, no need to reset pair->exit over again.

So better to have this improvement:

--- a/include/tst_fuzzy_sync.h
+++ b/include/tst_fuzzy_sync.h
@@ -232,7 +232,11 @@ static inline void tst_fzsync_pair_init(struct
tst_fzsync_pair *pair)
 static inline void tst_fzsync_pair_cleanup(struct tst_fzsync_pair *pair)
 {
        if (pair->thread_b) {
-               tst_atomic_store(1, &pair->exit);
+               /* Terminate thread B if parent hits accidental break */
+               if (!pair->exit) {
+                       tst_atomic_store(1, &pair->exit);
+                       usleep(100000);
+               }
                SAFE_PTHREAD_JOIN(pair->thread_b, NULL);
                pair->thread_b = 0;
        }
@@ -642,7 +646,6 @@ static inline void tst_fzsync_wait_b(struct
tst_fzsync_pair *pair)
  */
 static inline int tst_fzsync_run_a(struct tst_fzsync_pair *pair)
 {
-       int exit = 0;
        float rem_p = 1 - tst_timeout_remaining() / pair->exec_time_start;

        if ((pair->exec_time_p * SAMPLING_SLICE < rem_p)
@@ -657,19 +660,18 @@ static inline int tst_fzsync_run_a(struct
tst_fzsync_pair *pair)
        if (pair->exec_time_p < rem_p) {
                tst_res(TINFO,
                        "Exceeded execution time, requesting exit");
-               exit = 1;
+               tst_atomic_store(1, &pair->exit);
        }

        if (++pair->exec_loop > pair->exec_loops) {
                tst_res(TINFO,
                        "Exceeded execution loops, requesting exit");
-               exit = 1;
+               tst_atomic_store(1, &pair->exit);
        }

-       tst_atomic_store(exit, &pair->exit);
        tst_fzsync_wait_a(pair);

-       if (exit) {
+       if (pair->exit) {
                tst_fzsync_pair_cleanup(pair);
                return 0;
        }


-- 
Regards,
Li Wang
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linux.it/pipermail/ltp/attachments/20220407/4372028c/attachment.htm>