[PATCH] Fixes TLS performance degradation after dlopen

[Thomas Ilsche]

Hi,

this is a followup on a discussion and bug report from 2016.

https://sourceware.org/ml/libc-alpha/2016-06/threads.html#00203
https://sourceware.org/bugzilla/show_bug.cgi?id=19924

We have recently revisited this and the issue persists in the latest version and the patch still cleanly applies and fixes it. You can find a technical description as well as a minimal example in the bug report. I attached the patch again to this mail.

To recap what happened:

- Chris Metcalf, the original author of the patch for uclibc, said "we are good" from legal.
- Philipp Trommler (TU Dresden), who adapted the patch, signed the copyright form.
- There was a reference to bug 19329 whose patch touches the same code but it is a different correctness issue. It has not yet been merged.
- Adhemerval Zanella recently added to the bugtracker that the patch proposal should be discussed in libc-alpha for review.

This issue keeps biting us and I'd bet it happens to many others who don't know.

Is there anything we can do to move things forward?

Best,
Thomas
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