[PATCH 3/3] nptl: Fix race between pthread_kill and thread exit (bug 12889)

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> On 17/08/2021 10:51, Florian Weimer via Libc-alpha wrote:
>> Thread exit is delayed until all pending pthread_kill operations
>> on the thread have completed.  This avoids sending signals to the
>> wrong thread or a spurious ESRCH error.
>> 
>> The test sysdeps/pthread/tst-pthread_cancel-select-loop.c is derived
>> from a downstream test originally written by Marek Polacek.
>
> And I really hope we could first sort out the BZ#19951 and move away
> of using pthread::tid as the synchronization member to check thread
> termination.  I sent a possible fix [1], but it does not fully handle
> the pthread::tid access, it would require to a proper lock to 
> synchronize between thread exit and pthread_kill (as Rich has suggested
> on BZ#12889).
>
> I will need to send an updated version of my pthread fixes patchset,
> since clone3 changes broke it and INVALID_TD_P needs fixing as well.
>
> [1] https://patchwork.sourceware.org/project/glibc/patch/20210610193639.3650754-5-adhemerval.zanella@linaro.org/

I think my patch is independent of the other fixes.  Its advantage over
other proposals is that it does not add waiting to pthread_kill, so
there is no signal-safety issue.

(But I probably should test if cancellation from a signal handler that
is invoked synchronously via pthread_kill still works.)

Thanks,
Florian