diff options
Diffstat (limited to 'pkg/sentry/kernel')
| -rw-r--r-- | pkg/sentry/kernel/kernel.go | 129 | ||||
| -rw-r--r-- | pkg/sentry/kernel/posixtimer.go | 8 | ||||
| -rw-r--r-- | pkg/sentry/kernel/task_sched.go | 33 | ||||
| -rw-r--r-- | pkg/sentry/kernel/thread_group.go | 3 | ||||
| -rw-r--r-- | pkg/sentry/kernel/time/time.go | 27 |
5 files changed, 188 insertions, 12 deletions
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go index 8c1f79ab5..3cda03891 100644 --- a/pkg/sentry/kernel/kernel.go +++ b/pkg/sentry/kernel/kernel.go @@ -24,6 +24,7 @@ // TaskSet.mu // SignalHandlers.mu // Task.mu +// runningTasksMu // // Locking SignalHandlers.mu in multiple SignalHandlers requires locking // TaskSet.mu exclusively first. Locking Task.mu in multiple Tasks at the same @@ -135,6 +136,22 @@ type Kernel struct { // syslog is the kernel log. syslog syslog + // runningTasksMu synchronizes disable/enable of cpuClockTicker when + // the kernel is idle (runningTasks == 0). + // + // runningTasksMu is used to exclude critical sections when the timer + // disables itself and when the first active task enables the timer, + // ensuring that tasks always see a valid cpuClock value. + runningTasksMu sync.Mutex `state:"nosave"` + + // runningTasks is the total count of tasks currently in + // TaskGoroutineRunningSys or TaskGoroutineRunningApp. i.e., they are + // not blocked or stopped. + // + // runningTasks must be accessed atomically. Increments from 0 to 1 are + // further protected by runningTasksMu (see incRunningTasks). + runningTasks int64 + // cpuClock is incremented every linux.ClockTick. cpuClock is used to // measure task CPU usage, since sampling monotonicClock twice on every // syscall turns out to be unreasonably expensive. This is similar to how @@ -150,6 +167,22 @@ type Kernel struct { // cpuClockTicker increments cpuClock. cpuClockTicker *ktime.Timer `state:"nosave"` + // cpuClockTickerDisabled indicates that cpuClockTicker has been + // disabled because no tasks are running. + // + // cpuClockTickerDisabled is protected by runningTasksMu. + cpuClockTickerDisabled bool + + // cpuClockTickerSetting is the ktime.Setting of cpuClockTicker at the + // point it was disabled. It is cached here to avoid a lock ordering + // violation with cpuClockTicker.mu when runningTaskMu is held. + // + // cpuClockTickerSetting is only valid when cpuClockTickerDisabled is + // true. + // + // cpuClockTickerSetting is protected by runningTasksMu. + cpuClockTickerSetting ktime.Setting + // fdMapUids is an ever-increasing counter for generating FDTable uids. // // fdMapUids is mutable, and is accessed using atomic memory operations. @@ -912,6 +945,102 @@ func (k *Kernel) resumeTimeLocked() { } } +func (k *Kernel) incRunningTasks() { + for { + tasks := atomic.LoadInt64(&k.runningTasks) + if tasks != 0 { + // Standard case. Simply increment. + if !atomic.CompareAndSwapInt64(&k.runningTasks, tasks, tasks+1) { + continue + } + return + } + + // Transition from 0 -> 1. Synchronize with other transitions and timer. + k.runningTasksMu.Lock() + tasks = atomic.LoadInt64(&k.runningTasks) + if tasks != 0 { + // We're no longer the first task, no need to + // re-enable. + atomic.AddInt64(&k.runningTasks, 1) + k.runningTasksMu.Unlock() + return + } + + if !k.cpuClockTickerDisabled { + // Timer was never disabled. + atomic.StoreInt64(&k.runningTasks, 1) + k.runningTasksMu.Unlock() + return + } + + // We need to update cpuClock for all of the ticks missed while we + // slept, and then re-enable the timer. + // + // The Notify in Swap isn't sufficient. kernelCPUClockTicker.Notify + // always increments cpuClock by 1 regardless of the number of + // expirations as a heuristic to avoid over-accounting in cases of CPU + // throttling. + // + // We want to cover the normal case, when all time should be accounted, + // so we increment for all expirations. Throttling is less concerning + // here because the ticker is only disabled from Notify. This means + // that Notify must schedule and compensate for the throttled period + // before the timer is disabled. Throttling while the timer is disabled + // doesn't matter, as nothing is running or reading cpuClock anyways. + // + // S/R also adds complication, as there are two cases. Recall that + // monotonicClock will jump forward on restore. + // + // 1. If the ticker is enabled during save, then on Restore Notify is + // called with many expirations, covering the time jump, but cpuClock + // is only incremented by 1. + // + // 2. If the ticker is disabled during save, then after Restore the + // first wakeup will call this function and cpuClock will be + // incremented by the number of expirations across the S/R. + // + // These cause very different value of cpuClock. But again, since + // nothing was running while the ticker was disabled, those differences + // don't matter. + setting, exp := k.cpuClockTickerSetting.At(k.monotonicClock.Now()) + if exp > 0 { + atomic.AddUint64(&k.cpuClock, exp) + } + + // Now that cpuClock is updated it is safe to allow other tasks to + // transition to running. + atomic.StoreInt64(&k.runningTasks, 1) + + // N.B. we must unlock before calling Swap to maintain lock ordering. + // + // cpuClockTickerDisabled need not wait until after Swap to become + // true. It is sufficient that the timer *will* be enabled. + k.cpuClockTickerDisabled = false + k.runningTasksMu.Unlock() + + // This won't call Notify (unless it's been ClockTick since setting.At + // above). This means we skip the thread group work in Notify. However, + // since nothing was running while we were disabled, none of the timers + // could have expired. + k.cpuClockTicker.Swap(setting) + + return + } +} + +func (k *Kernel) decRunningTasks() { + tasks := atomic.AddInt64(&k.runningTasks, -1) + if tasks < 0 { + panic(fmt.Sprintf("Invalid running count %d", tasks)) + } + + // Nothing to do. The next CPU clock tick will disable the timer if + // there is still nothing running. This provides approximately one tick + // of slack in which we can switch back and forth between idle and + // active without an expensive transition. +} + // WaitExited blocks until all tasks in k have exited. func (k *Kernel) WaitExited() { k.tasks.liveGoroutines.Wait() diff --git a/pkg/sentry/kernel/posixtimer.go b/pkg/sentry/kernel/posixtimer.go index c5d095af7..2e861a5a8 100644 --- a/pkg/sentry/kernel/posixtimer.go +++ b/pkg/sentry/kernel/posixtimer.go @@ -117,9 +117,9 @@ func (it *IntervalTimer) signalRejectedLocked() { } // Notify implements ktime.TimerListener.Notify. -func (it *IntervalTimer) Notify(exp uint64) { +func (it *IntervalTimer) Notify(exp uint64, setting ktime.Setting) (ktime.Setting, bool) { if it.target == nil { - return + return ktime.Setting{}, false } it.target.tg.pidns.owner.mu.RLock() @@ -129,7 +129,7 @@ func (it *IntervalTimer) Notify(exp uint64) { if it.sigpending { it.overrunCur += exp - return + return ktime.Setting{}, false } // sigpending must be set before sendSignalTimerLocked() so that it can be @@ -148,6 +148,8 @@ func (it *IntervalTimer) Notify(exp uint64) { if err := it.target.sendSignalTimerLocked(si, it.group, it); err != nil { it.signalRejectedLocked() } + + return ktime.Setting{}, false } // Destroy implements ktime.TimerListener.Destroy. Users of Timer should call diff --git a/pkg/sentry/kernel/task_sched.go b/pkg/sentry/kernel/task_sched.go index e76c069b0..8b148db35 100644 --- a/pkg/sentry/kernel/task_sched.go +++ b/pkg/sentry/kernel/task_sched.go @@ -126,12 +126,22 @@ func (t *Task) accountTaskGoroutineEnter(state TaskGoroutineState) { t.gosched.Timestamp = now t.gosched.State = state t.goschedSeq.EndWrite() + + if state != TaskGoroutineRunningApp { + // Task is blocking/stopping. + t.k.decRunningTasks() + } } // Preconditions: The caller must be running on the task goroutine, and leaving // a state indicated by a previous call to // t.accountTaskGoroutineEnter(state). func (t *Task) accountTaskGoroutineLeave(state TaskGoroutineState) { + if state != TaskGoroutineRunningApp { + // Task is unblocking/continuing. + t.k.incRunningTasks() + } + now := t.k.CPUClockNow() if t.gosched.State != state { panic(fmt.Sprintf("Task goroutine switching from state %v (expected %v) to %v", t.gosched.State, state, TaskGoroutineRunningSys)) @@ -330,7 +340,7 @@ func newKernelCPUClockTicker(k *Kernel) *kernelCPUClockTicker { } // Notify implements ktime.TimerListener.Notify. -func (ticker *kernelCPUClockTicker) Notify(exp uint64) { +func (ticker *kernelCPUClockTicker) Notify(exp uint64, setting ktime.Setting) (ktime.Setting, bool) { // Only increment cpuClock by 1 regardless of the number of expirations. // This approximately compensates for cases where thread throttling or bad // Go runtime scheduling prevents the kernelCPUClockTicker goroutine, and @@ -426,6 +436,27 @@ func (ticker *kernelCPUClockTicker) Notify(exp uint64) { tgs[i] = nil } ticker.tgs = tgs[:0] + + // If nothing is running, we can disable the timer. + tasks := atomic.LoadInt64(&ticker.k.runningTasks) + if tasks == 0 { + ticker.k.runningTasksMu.Lock() + defer ticker.k.runningTasksMu.Unlock() + tasks := atomic.LoadInt64(&ticker.k.runningTasks) + if tasks != 0 { + // Raced with a 0 -> 1 transition. + return setting, false + } + + // Stop the timer. We must cache the current setting so the + // kernel can access it without violating the lock order. + ticker.k.cpuClockTickerSetting = setting + ticker.k.cpuClockTickerDisabled = true + setting.Enabled = false + return setting, true + } + + return setting, false } // Destroy implements ktime.TimerListener.Destroy. diff --git a/pkg/sentry/kernel/thread_group.go b/pkg/sentry/kernel/thread_group.go index 0eef24bfb..72568d296 100644 --- a/pkg/sentry/kernel/thread_group.go +++ b/pkg/sentry/kernel/thread_group.go @@ -511,8 +511,9 @@ type itimerRealListener struct { } // Notify implements ktime.TimerListener.Notify. -func (l *itimerRealListener) Notify(exp uint64) { +func (l *itimerRealListener) Notify(exp uint64, setting ktime.Setting) (ktime.Setting, bool) { l.tg.SendSignal(SignalInfoPriv(linux.SIGALRM)) + return ktime.Setting{}, false } // Destroy implements ktime.TimerListener.Destroy. diff --git a/pkg/sentry/kernel/time/time.go b/pkg/sentry/kernel/time/time.go index aa6c75d25..107394183 100644 --- a/pkg/sentry/kernel/time/time.go +++ b/pkg/sentry/kernel/time/time.go @@ -280,13 +280,16 @@ func (ClockEventsQueue) Readiness(mask waiter.EventMask) waiter.EventMask { // A TimerListener receives expirations from a Timer. type TimerListener interface { // Notify is called when its associated Timer expires. exp is the number of - // expirations. + // expirations. setting is the next timer Setting. // // Notify is called with the associated Timer's mutex locked, so Notify // must not take any locks that precede Timer.mu in lock order. // + // If Notify returns true, the timer will use the returned setting + // rather than the passed one. + // // Preconditions: exp > 0. - Notify(exp uint64) + Notify(exp uint64, setting Setting) (newSetting Setting, update bool) // Destroy is called when the timer is destroyed. Destroy() @@ -533,7 +536,9 @@ func (t *Timer) Tick() { s, exp := t.setting.At(now) t.setting = s if exp > 0 { - t.listener.Notify(exp) + if newS, ok := t.listener.Notify(exp, t.setting); ok { + t.setting = newS + } } t.resetKickerLocked(now) } @@ -588,7 +593,9 @@ func (t *Timer) Get() (Time, Setting) { s, exp := t.setting.At(now) t.setting = s if exp > 0 { - t.listener.Notify(exp) + if newS, ok := t.listener.Notify(exp, t.setting); ok { + t.setting = newS + } } t.resetKickerLocked(now) return now, s @@ -620,7 +627,9 @@ func (t *Timer) SwapAnd(s Setting, f func()) (Time, Setting) { } oldS, oldExp := t.setting.At(now) if oldExp > 0 { - t.listener.Notify(oldExp) + t.listener.Notify(oldExp, oldS) + // N.B. The returned Setting doesn't matter because we're about + // to overwrite. } if f != nil { f() @@ -628,7 +637,9 @@ func (t *Timer) SwapAnd(s Setting, f func()) (Time, Setting) { newS, newExp := s.At(now) t.setting = newS if newExp > 0 { - t.listener.Notify(newExp) + if newS, ok := t.listener.Notify(newExp, t.setting); ok { + t.setting = newS + } } t.resetKickerLocked(now) return now, oldS @@ -683,11 +694,13 @@ func NewChannelNotifier() (TimerListener, <-chan struct{}) { } // Notify implements ktime.TimerListener.Notify. -func (c *ChannelNotifier) Notify(uint64) { +func (c *ChannelNotifier) Notify(uint64, Setting) (Setting, bool) { select { case c.tchan <- struct{}{}: default: } + + return Setting{}, false } // Destroy implements ktime.TimerListener.Destroy and will close the channel. |