[PATCH] nptl: Fix deadlock on atfork handler which calls dlclose (BZ#24595)

[Florian Weimer]

I have thought about this some more and now wonder if we should add a
generic copy-on-write list which supports deletions in the middle.

We could use it for an internal copy of _IO_list_all (which is
unfortunately part of the ABI), too.  It would help with code that has
to deal with callbacks where the callbacks can acquire the list lock or
modify the list.

Thanks,
Florian