CVSROOT: /cvs Module name: src Changes by: chel...@cvs.openbsd.org 2019/03/25 17:32:00
Modified files: sys/kern : kern_tc.c kern_time.c sys/sys : timetc.h Log message: MP-safe timecounting: new rwlock: tc_lock tc_lock allows adjfreq(2) and the kern.timecounter.hardware sysctl(2) to read/write the active timecounter pointer and the .tc_adj_freq member of the active timecounter safely. This eliminates any possibility of a torn read/write for the .tc_adj_freq member when we drop the KERNEL_LOCK from the timecounting layer. It also ensures the active timecounter does not change in the midst of an adjfreq(2) call. Because these are not high-traffic paths, we can get away with using tc_lock in write-mode to ensure combination read/write adjtime(2) calls are relatively atomic (a) to other writer adjtime(2) calls, and (b) to settimeofday(2)/clock_settime(2) calls, which cancel ongoing adjtime(2) adjustment. When the KERNEL_LOCK is dropped, an unprivileged user will be able to create some tc_lock contention via adjfreq(2); it is very unlikely to ever be a problem. If it ever is actually a problem a lockless read could be added to address it. While here, reorganize sys_adjfreq()/sys_adjtime() to minimize code under the lock. Also while here, make tc_adjfreq() void, as it cannot fail under any circumstance. Also also while here, annotate various globals/struct members with lock ordering details. With lots of input from mpi@ and visa@. ok visa@