From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexey Kodanev <aleksei.kodanev@bell-sw.com>
Date: Fri, 16 Jul 2021 15:12:58 +0300
Subject: [LTP] [PATCH] crypto/af_alg02: use pthread_tryjoin_np() instead
 of pthread_kill()
In-Reply-To: <YPFWn+/sbK1vlJKt@pevik>
References: <20210715102813.106843-1-aleksei.kodanev@bell-sw.com>
 <CAEemH2cXAY8KSFNNv8_23uSs-wRaResAkTPmPyZQNN6UwcMcgA@mail.gmail.com>
 <YPFWn+/sbK1vlJKt@pevik>
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Hi Petr,
On 16.07.2021 12:51, Petr Vorel wrote:
>> Hi Alexey,
> 
>> On Thu, Jul 15, 2021 at 6:29 PM Alexey Kodanev <aleksei.kodanev@bell-sw.com>
>> wrote:
> 
>>> musl doesn't return ESRCH for pthread_kill() if thread id is not found.
> Maybe ask on MUSL mailing list?

It's not a musl issue, but I was going to send a few improvements (including
this) when time permits.

> 
>>> POSIX only recommends to return ESRCH, and also says that pthread_kill()
>>> produces undefined behavior if tid lifetime has ended [1].
> 
>>> [1]: https://man7.org/linux/man-pages/man3/pthread_kill.3.html
> 
>>> Signed-off-by: Alexey Kodanev <aleksei.kodanev@bell-sw.com>
>>> ---
>>>  testcases/kernel/crypto/af_alg02.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
>>> diff --git a/testcases/kernel/crypto/af_alg02.c
>>> b/testcases/kernel/crypto/af_alg02.c
>>> index 31d30777c..0f5793c16 100644
>>> --- a/testcases/kernel/crypto/af_alg02.c
>>> +++ b/testcases/kernel/crypto/af_alg02.c
>>> @@ -60,7 +60,7 @@ static void run(void)
> 
>>>         TST_CHECKPOINT_WAIT(0);
> 
>>> -       while (pthread_kill(thr, 0) != ESRCH) {
>>> +       while (pthread_tryjoin_np(thr, NULL) == EBUSY) {
> 
> 
>> I'm not sure if safe enough to use because it is nonstandard GNU extensions
>> and the "_np" means nonportable.
> Others please double check, but pthread_tryjoin_np() seems to be in uclibc-ng
> and musl (+ of course in glibc). It's only missing in bionic (it looks like
> people would like to have it [1]).
> 

Yeah, I think it's quite useful.

>> Maybe another workaround is to define a volatile flag 'thread_complete',
>> initialize it to '0' when thread_B starts and reset to '1' while exit, and
>> just
>> do a value check in the while loop of thread_A should acquire thread_B
>> status.
>> Is this way a bit better?
> Sounds as reasonable workaround for me.
> 
> Kind regards,
> Petr
> 
> [1] https://github.com/kito-cheng/android-checkpoint/blob/master/bionic/0003-bionic-Implement-pthread_tryjoin_np.patch
>