[PATCH]: Fix blocking pthread_join.

[Stefan Liebler]

On 05/02/2018 06:27 AM, Carlos O'Donell wrote:
> On 04/30/2018 11:19 AM, Stefan Liebler wrote:
>> diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
>> index 8326e2805c..bfbda99940 100644
>> --- a/sysdeps/nptl/lowlevellock.h
>> +++ b/sysdeps/nptl/lowlevellock.h
>> @@ -181,11 +181,14 @@ extern int __lll_timedlock_wait (int *futex, const struct timespec *,
>>      thread ID while the clone is running and is reset to zero by the kernel
>>      afterwards.  The kernel up to version 3.16.3 does not use the private futex
>>      operations for futex wake-up when the clone terminates.  */
>> -#define lll_wait_tid(tid) \
>> -  do {					\
>> -    __typeof (tid) __tid;		\
>> -    while ((__tid = (tid)) != 0)	\
>> -      lll_futex_wait (&(tid), __tid, LLL_SHARED);\
>> +#define lll_wait_tid(tid)				\
>> +  do {							\
>> +    __typeof (tid) __tid;				\
>> +    /* We need acquire MO here so that we synchronize	\
>> +       with the kernel's store to 0 when the clone	\
>> +       terminates. (see above)  */			\
>> +    while ((__tid = atomic_load_acquire (&(tid))) != 0)	\
>> +      lll_futex_wait (&(tid), __tid, LLL_SHARED);	\
>>     } while (0)
>>   
>>   extern int __lll_timedwait_tid (int *, const struct timespec *)
> 
> This looks good to me, and improves the situation.
> 
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> 
I've just committed this part and opened the
"Bug 23137 - s390: pthread_join sometimes block indefinitely (on 31bit 
and libc build with -Os)"
(https://sourceware.org/bugzilla/show_bug.cgi?id=23137)

> I haven't had a chance to review the other P&C issues discussed by Torvald,
> but we should probably raise them in a new thread related to tid reloading
> and the consequences.
>