diff options
Diffstat (limited to 'lib/libc/sys/__vdso_gettimeofday.c')
| -rw-r--r-- | lib/libc/sys/__vdso_gettimeofday.c | 25 |
1 files changed, 14 insertions, 11 deletions
diff --git a/lib/libc/sys/__vdso_gettimeofday.c b/lib/libc/sys/__vdso_gettimeofday.c index a305173b3ed8c..b3527fa4de533 100644 --- a/lib/libc/sys/__vdso_gettimeofday.c +++ b/lib/libc/sys/__vdso_gettimeofday.c @@ -42,6 +42,15 @@ tc_delta(const struct vdso_timehands *th) th->th_counter_mask); } +/* + * Calculate the absolute or boot-relative time from the + * machine-specific fast timecounter and the published timehands + * structure read from the shared page. + * + * The lockless reading scheme is similar to the one used to read the + * in-kernel timehands, see sys/kern/kern_tc.c:binuptime(). This code + * is based on the kernel implementation. + */ static int binuptime(struct bintime *bt, struct vdso_timekeep *tk, int abs) { @@ -52,27 +61,21 @@ binuptime(struct bintime *bt, struct vdso_timekeep *tk, int abs) if (!tk->tk_enabled) return (ENOSYS); - /* - * XXXKIB. The load of tk->tk_current should use - * atomic_load_acq_32 to provide load barrier. But - * since tk points to r/o mapped page, x86 - * implementation of atomic_load_acq faults. - */ - curr = tk->tk_current; - rmb(); + curr = atomic_load_acq_32(&tk->tk_current); th = &tk->tk_th[curr]; if (th->th_algo != VDSO_TH_ALGO_1) return (ENOSYS); - gen = th->th_gen; + gen = atomic_load_acq_32(&th->th_gen); *bt = th->th_offset; bintime_addx(bt, th->th_scale * tc_delta(th)); if (abs) bintime_add(bt, &th->th_boottime); /* - * Barrier for load of both tk->tk_current and th->th_gen. + * Ensure that the load of th_offset is completed + * before the load of th_gen. */ - rmb(); + atomic_thread_fence_acq(); } while (curr != tk->tk_current || gen == 0 || gen != th->th_gen); return (0); } |