Re: lib/59751 (dlclose is not MT-safe depending on the libraries unloaded)

[riastradh%NetBSD.org@localhost]

Synopsis: dlclose is not MT-safe depending on the libraries unloaded

Responsible-Changed-From-To: lib-bug-people->riastradh
Responsible-Changed-By: riastradh%NetBSD.org@localhost
Responsible-Changed-When: Sun, 23 Nov 2025 22:30:02 +0000
Responsible-Changed-Why:
mine


State-Changed-From-To: open->analyzed
State-Changed-By: riastradh%NetBSD.org@localhost
State-Changed-When: Sun, 23 Nov 2025 22:30:02 +0000
State-Changed-Why:
The main culprit is that while dlopen and dlclose are mostly serialized
by the rtld exclusive lock, they drop that lock to call constructors
and destructors -- and when that happens, they can get interleaved and
observe troublesome intermediate states.

I added a test case for this, and drafted a patch to address this by
serializing the constructor and destructor calls and deferring
unmapping/freeing objects until any concurrent dlclose activity on them
has completed -- could stand some more review and testing before I
commit:

https://mollari.NetBSD.org/~riastradh/tmp/20251122/pr59751-dlcloserace-v2.patch
https://mollari.NetBSD.org/~riastradh/tmp/20251122/pr59751-dlcloserace-v2.diff