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Differential D50117

thr_rtld: accept read lock requests while owning the lock for write
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Authored by kib on May 2 2025, 3:38 PM.
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markj
olce
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rG812c4bf3f170: thr_rtld: accept read lock requests while owning the lock for write
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PR: 286505

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rG FreeBSD src repository
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kib created this revision.May 2 2025, 3:38 PM
Herald added a subscriber: imp. · View Herald TranscriptMay 2 2025, 3:38 PM
kib requested review of this revision.May 2 2025, 3:38 PM
olce accepted this revision.May 2 2025, 4:15 PM

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?

This revision is now accepted and ready to land.May 2 2025, 4:15 PM
kib added a comment.May 2 2025, 5:41 PM
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.

Closed by commit rG812c4bf3f170: thr_rtld: accept read lock requests while owning the lock for write (authored by kib). · Explain WhyMay 2 2025, 6:09 PM
This revision was automatically updated to reflect the committed changes.
kib added a commit: rG812c4bf3f170: thr_rtld: accept read lock requests while owning the lock for write.
olce added a comment.May 2 2025, 7:22 PM

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.

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lib/libthr/thread/thr_rtld.c

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