thr_rtld: accept read lock requests while owning the lock for write

[kib]

Summary

PR: 286505

[olce]

The logic appears fine. Out of curiosity, could you describe or provide some links to the context of this change? I think I saw several changes passing in rtld recently, but haven't followed.

lib/libthr/thread/thr_rtld.c

175–182

That trick extends the write lock as seen by other threads until all the references from the locking thread have been released (write but also read). Could that be a problem?

[kib]

In D50117#1143243, @olce wrote:

The logic appears fine. Out of curiosity, could you describe or provide some links to the context of this change? I think I saw several changes passing in rtld recently, but haven't followed.

See the referenced PR for the test case.

lib/libthr/thread/thr_rtld.c

175–182

This is the expected behavior, how could it be different? The last reference releases the exclusive/write lock.

[olce]

Thanks, I hadn't seen it above.

lib/libthr/thread/thr_rtld.c

175–182

I was just wondering if that could be a problem in the context of the change. I do indeed see no other way without splitting _thr_rtld_lock_release() into 2 functions, one for the write lock and another one for read locks.