CVE-2026-74446: drm/amdkfd: hold event_mutex while checkpointing CRIU events

In the Linux kernel, the following vulnerability has been resolved:

drm/amdkfd: hold eventmutex while checkpointing CRIU events

kfdcriucheckpointevents() counts the entries in p->eventidr via kfdgetnumevents(), allocates an array sized to that count, and then walks the same IDR to fill it. Neither the count nor the walk holds p->eventmutex.

The CRIU checkpoint caller holds only p->mutex. Event create and destroy (kfdeventcreate()/kfdeventdestroy()) take p->eventmutex and do not take p->mutex, so a second thread in the same process can insert or remove events between the count and the walk. If an event is inserted, the walk iterates more entries than were counted and writes past the end of the evprivs allocation; if an event is removed, the walk dereferences an entry that is being freed.

Hold p->eventmutex across the count and the walk so both observe a consistent view of p->eventidr. The lock is released before copytouser(), which only touches the local buffer. The caller already holds p->mutex and the create/destroy paths never take p->mutex, so the p->mutex -> p->eventmutex order is not inverted and no deadlock is introduced.

(cherry picked from commit ff57e223ab105795b05d3ef3f3c35a5a441bcbaa)