CVSROOT: /cvs
Module name: src
Changes by: v...@cvs.openbsd.org 2025/04/14 03:14:51
Modified files:
sys/kern : subr_witness.c
sys/sys : _lock.h witness.h
Log message:
witness: Improve handling of lock nesting
Add an option to specify a parent/child lock relation for a lock object.
This lets witness(4) handle the nesting of locks that have the same type
without using LO_DUPOK or LOP_DUPOK.
An example: The states of objects o1 and o2 are protected by locks
o1->o_mtx and o2->o_mtx, respectively. The objects are hierarchical
and there is an operation that requires keeping them both locked at the
same time. Assume the hierarchy mandates that o1 is locked first.
The duplicate locking error can now be avoided by using
WITNESS_SETCHILD(&o1->o_mtx.lock_object, &o2->o_mtx.lock_object)
or
WITNESS_SETPARENT(&o2->o_mtx.lock_object, &o1->o_mtx.lock_object)
after the lock initializer.
The choice between WITNESS_SETCHILD() and WITNESS_SETPARENT() depends
on whether the object access pattern is many-to-one or one-to-many from
locking perspective; the implementation allows only one predefined
parent/child relation per lock.
OK mpi@, claudio@ (earlier version)
