[PATCH] Fix rwlock stall with PREFER_WRITER_NONRECURSIVE_NP (bug 23861)

[Andreas Schwab]

On Dez 11 2018, Florian Weimer <fweimer@redhat.com> wrote:

> * Andreas Schwab:
>
>> On Dez 11 2018, Florian Weimer <fweimer@redhat.com> wrote:
>>
>>> * Andreas Schwab:
>>>
>>>> +volatile int do_exit;
>>>
>>> Please no volatile, and use the GCC __atomic builtins instead (not the
>>> glibc-internal ones, which are inaccessible).
>>
>> It's only about the compiler not optimizing the access, no atomicity
>> required.
>
> No, without atomics, the code has a data race and undefined behavior.

In which way?  There is a single setter, and it doesn't matter how long
the thread takes to see the transition from zero to non-zero.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."