[LTP] [PATCH] syscalls/futex_waitv03: replace TST_THREAD_STATE_WAIT with repeated wake

[Jan Stancek]

On Mon, Jul 11, 2022 at 9:17 AM Li Wang <liwang@redhat.com> wrote:
>
>
>
> On Fri, Jul 8, 2022 at 12:56 AM Jan Stancek <jstancek@redhat.com> wrote:
>>
>> TST_THREAD_STATE_WAIT isn't reliable to tell that it's safe to call futex_wake().
>> futex_wake() can be called prematurely and return 0, which leaves other thread
>> timing out on futex call:
>>   tst_test.c:1459: TINFO: Timeout per run is 0h 10m 00s
>>   futex_waitv03.c:37: TINFO: Testing variant: syscall with old kernel spec
>>   tst_buffers.c:55: TINFO: Test is using guarded buffers
>>   futex_waitv03.c:106: TBROK: futex_waitv returned: -1: ETIMEDOUT (110)
>>
>> Replace it with repeated futex_wake() until it fails or wakes at least 1 waiter.
>> Also extend timeout to 5 seconds to avoid false positives from systems with
>> high steal time (e.g. overloaded s390x host).
>
>
> Though TST_THREAD_STATE_WAIT is unreliable, I guess that would
> still add more chances if we keep it?
> (I mean go with repeat futex_wake() after checking 'S' state)

We could keep it, though I'm not sure what benefit that has. You
would probably make fewer calls to futex_wake(). Without it,
the window where wake and wait calls are made in parallel
is larger, and it also makes test simpler.