On 2023-04-21 17:30:24 [+0200], Thomas Gleixner wrote:
The out-of-tree RT patches make extensive use of the code. Since it is upstream code, I assumed it should go via the official stable trees. Without RT, the code is limited the rt_mutex_lock() used by I2C and the RCU booster-mutex.
Which is a reason to route it through the upstream stable trees, no?
I do not understand. Why would we take a patch in the stable tree because an out-of-tree change requires it?
The change is to the rtmutex core which _IS_ used in tree by futex, RCU and some drivers.
not back stab but to clarify: futex does not use the annotation (it does not use the fastpath) but RCU-boosting _and_ I2C-bus code does use it.
So both mainline users users of the rtmutex code are affected.
Just because the problem was observed on RT it does not make the mainline usage of RTMUTEXes magically unaffected. The missing acquire semantics are required there too.
Thanks,
tglx
Sebastian