diff options
Diffstat (limited to 'kernel/time/hrtimer.c')
| -rw-r--r-- | kernel/time/hrtimer.c | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 90dcc4d95e91..c101f88ae8aa 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1676,6 +1676,16 @@ static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer) void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl, enum hrtimer_mode mode) { + /* + * Make the enqueue delivery mode check work on RT. If the sleeper + * was initialized for hard interrupt delivery, force the mode bit. + * This is a special case for hrtimer_sleepers because + * hrtimer_init_sleeper() determines the delivery mode on RT so the + * fiddling with this decision is avoided at the call sites. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && sl->timer.is_hard) + mode |= HRTIMER_MODE_HARD; + hrtimer_start_expires(&sl->timer, mode); } EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires); @@ -1683,6 +1693,30 @@ EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires); static void __hrtimer_init_sleeper(struct hrtimer_sleeper *sl, clockid_t clock_id, enum hrtimer_mode mode) { + /* + * On PREEMPT_RT enabled kernels hrtimers which are not explicitely + * marked for hard interrupt expiry mode are moved into soft + * interrupt context either for latency reasons or because the + * hrtimer callback takes regular spinlocks or invokes other + * functions which are not suitable for hard interrupt context on + * PREEMPT_RT. + * + * The hrtimer_sleeper callback is RT compatible in hard interrupt + * context, but there is a latency concern: Untrusted userspace can + * spawn many threads which arm timers for the same expiry time on + * the same CPU. That causes a latency spike due to the wakeup of + * a gazillion threads. + * + * OTOH, priviledged real-time user space applications rely on the + * low latency of hard interrupt wakeups. If the current task is in + * a real-time scheduling class, mark the mode for hard interrupt + * expiry. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + if (task_is_realtime(current) && !(mode & HRTIMER_MODE_SOFT)) + mode |= HRTIMER_MODE_HARD; + } + __hrtimer_init(&sl->timer, clock_id, mode); sl->timer.function = hrtimer_wakeup; sl->task = current; |