[PATCH v2] Fix double-checked locking in __gconv_get_path and __gconv_read_conf [BZ #22062]

[Florian Weimer]

On 10/06/2017 01:05 AM, Carlos O'Donell wrote:
> Is there any reason we need this atomic load?
> 
>> +      gconv_path_elem_local = atomic_load_relaxed (&__gconv_path_elem);
>                                   ^^^^^^^^^^^^^^^^^^^

Oh, this follows just the general rule that if atomics are used, all 
accesses should employ atomics.  This follows from the general principle 
of C11 compatibility, where an atomic type would default to seq-cst 
access (which we don't want here).  I see this was not mentioned in the 
Concurrency wiki page.  I've fixed that.

I did not notice that there was a __libc_once guard.  So it would be 
better to remove the locking from __gconv_get_path and document that 
(including that this serializes initialization of the gconv cache via 
__gconv_load_cache).

Thanks,
Florian