Add runtime tracing.

This adds meaningful annotations to the trace generated by the runtime/trace
package.

PiperOrigin-RevId: 284290115

12 files changed, 171 insertions, 21 deletions

diff --git a/pkg/sentry/control/pprof.go b/pkg/sentry/control/pprof.go
index 1f78d54a2..e1f2fea60 100644
--- a/pkg/sentry/control/pprof.go
+++ b/pkg/sentry/control/pprof.go
@@ -22,6 +22,7 @@ import (
 	"sync"
 
 	"gvisor.dev/gvisor/pkg/fd"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/urpc"
 )
 
@@ -56,6 +57,9 @@ type Profile struct {
 
 	// traceFile is the current execution trace output file.
 	traceFile *fd.FD
+
+	// Kernel is the kernel under profile.
+	Kernel *kernel.Kernel
 }
 
 // StartCPUProfile is an RPC stub which starts recording the CPU profile in a
@@ -147,6 +151,9 @@ func (p *Profile) StartTrace(o *ProfileOpts, _ *struct{}) error {
 		return err
 	}
 
+	// Ensure all trace contexts are registered.
+	p.Kernel.RebuildTraceContexts()
+
 	p.traceFile = output
 	return nil
 }
@@ -158,9 +165,15 @@ func (p *Profile) StopTrace(_, _ *struct{}) error {
 	defer p.mu.Unlock()
 
 	if p.traceFile == nil {
-		return errors.New("Execution tracing not start")
+		return errors.New("Execution tracing not started")
 	}
 
+	// Similarly to the case above, if tasks have not ended traces, we will
+	// lose information. Thus we need to rebuild the tasks in order to have
+	// complete information. This will not lose information if multiple
+	// traces are overlapping.
+	p.Kernel.RebuildTraceContexts()
+
 	trace.Stop()
 	p.traceFile.Close()
 	p.traceFile = nil
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 28ba950bd..bd3fb4c03 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -841,9 +841,11 @@ func (k *Kernel) CreateProcess(args CreateProcessArgs) (*ThreadGroup, ThreadID,
 		AbstractSocketNamespace: args.AbstractSocketNamespace,
 		ContainerID:             args.ContainerID,
 	}
-	if _, err := k.tasks.NewTask(config); err != nil {
+	t, err := k.tasks.NewTask(config)
+	if err != nil {
 		return nil, 0, err
 	}
+	t.traceExecEvent(tc) // Simulate exec for tracing.
 
 	// Success.
 	tgid := k.tasks.Root.IDOfThreadGroup(tg)
@@ -1118,6 +1120,22 @@ func (k *Kernel) SendContainerSignal(cid string, info *arch.SignalInfo) error {
 	return lastErr
 }
 
+// RebuildTraceContexts rebuilds the trace context for all tasks.
+//
+// Unfortunately, if these are built while tracing is not enabled, then we will
+// not have meaningful trace data. Rebuilding here ensures that we can do so
+// after tracing has been enabled.
+func (k *Kernel) RebuildTraceContexts() {
+	k.extMu.Lock()
+	defer k.extMu.Unlock()
+	k.tasks.mu.RLock()
+	defer k.tasks.mu.RUnlock()
+
+	for t, tid := range k.tasks.Root.tids {
+		t.rebuildTraceContext(tid)
+	}
+}
+
 // FeatureSet returns the FeatureSet.
 func (k *Kernel) FeatureSet() *cpuid.FeatureSet {
 	return k.featureSet
diff --git a/pkg/sentry/kernel/syscalls.go b/pkg/sentry/kernel/syscalls.go
index 220fa73a2..2fdee0282 100644
--- a/pkg/sentry/kernel/syscalls.go
+++ b/pkg/sentry/kernel/syscalls.go
@@ -339,6 +339,14 @@ func (s *SyscallTable) Lookup(sysno uintptr) SyscallFn {
 	return nil
 }
 
+// LookupName looks up a syscall name.
+func (s *SyscallTable) LookupName(sysno uintptr) string {
+	if sc, ok := s.Table[sysno]; ok {
+		return sc.Name
+	}
+	return fmt.Sprintf("sys_%d", sysno) // Unlikely.
+}
+
 // LookupEmulate looks up an emulation syscall number.
 func (s *SyscallTable) LookupEmulate(addr usermem.Addr) (uintptr, bool) {
 	sysno, ok := s.Emulate[addr]
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index 80c8e5464..ab0c6c4aa 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -15,6 +15,8 @@
 package kernel
 
 import (
+	gocontext "context"
+	"runtime/trace"
 	"sync"
 	"sync/atomic"
 
@@ -390,7 +392,14 @@ type Task struct {
 
 	// logPrefix is a string containing the task's thread ID in the root PID
 	// namespace, and is prepended to log messages emitted by Task.Infof etc.
-	logPrefix atomic.Value `state:".(string)"`
+	logPrefix atomic.Value `state:"nosave"`
+
+	// traceContext and traceTask are both used for tracing, and are
+	// updated along with the logPrefix in updateInfoLocked.
+	//
+	// These are exclusive to the task goroutine.
+	traceContext gocontext.Context `state:"nosave"`
+	traceTask    *trace.Task       `state:"nosave"`
 
 	// creds is the task's credentials.
 	//
@@ -528,14 +537,6 @@ func (t *Task) loadPtraceTracer(tracer *Task) {
 	t.ptraceTracer.Store(tracer)
 }
 
-func (t *Task) saveLogPrefix() string {
-	return t.logPrefix.Load().(string)
-}
-
-func (t *Task) loadLogPrefix(prefix string) {
-	t.logPrefix.Store(prefix)
-}
-
 func (t *Task) saveSyscallFilters() []bpf.Program {
 	if f := t.syscallFilters.Load(); f != nil {
 		return f.([]bpf.Program)
@@ -549,6 +550,7 @@ func (t *Task) loadSyscallFilters(filters []bpf.Program) {
 
 // afterLoad is invoked by stateify.
 func (t *Task) afterLoad() {
+	t.updateInfoLocked()
 	t.interruptChan = make(chan struct{}, 1)
 	t.gosched.State = TaskGoroutineNonexistent
 	if t.stop != nil {
diff --git a/pkg/sentry/kernel/task_block.go b/pkg/sentry/kernel/task_block.go
index dd69939f9..4a4a69ee2 100644
--- a/pkg/sentry/kernel/task_block.go
+++ b/pkg/sentry/kernel/task_block.go
@@ -16,6 +16,7 @@ package kernel
 
 import (
 	"runtime"
+	"runtime/trace"
 	"time"
 
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
@@ -133,19 +134,24 @@ func (t *Task) block(C <-chan struct{}, timerChan <-chan struct{}) error {
 		runtime.Gosched()
 	}
 
+	region := trace.StartRegion(t.traceContext, blockRegion)
 	select {
 	case <-C:
+		region.End()
 		t.SleepFinish(true)
+		// Woken by event.
 		return nil
 
 	case <-interrupt:
+		region.End()
 		t.SleepFinish(false)
 		// Return the indicated error on interrupt.
 		return syserror.ErrInterrupted
 
 	case <-timerChan:
-		// We've timed out.
+		region.End()
 		t.SleepFinish(true)
+		// We've timed out.
 		return syserror.ETIMEDOUT
 	}
 }
diff --git a/pkg/sentry/kernel/task_clone.go b/pkg/sentry/kernel/task_clone.go
index 0916fd658..3eadfedb4 100644
--- a/pkg/sentry/kernel/task_clone.go
+++ b/pkg/sentry/kernel/task_clone.go
@@ -299,6 +299,7 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 	// nt that it must receive before its task goroutine starts running.
 	tid := nt.k.tasks.Root.IDOfTask(nt)
 	defer nt.Start(tid)
+	t.traceCloneEvent(tid)
 
 	// "If fork/clone and execve are allowed by @prog, any child processes will
 	// be constrained to the same filters and system call ABI as the parent." -
diff --git a/pkg/sentry/kernel/task_exec.go b/pkg/sentry/kernel/task_exec.go
index 17a089b90..90a6190f1 100644
--- a/pkg/sentry/kernel/task_exec.go
+++ b/pkg/sentry/kernel/task_exec.go
@@ -129,6 +129,7 @@ type runSyscallAfterExecStop struct {
 }
 
 func (r *runSyscallAfterExecStop) execute(t *Task) taskRunState {
+	t.traceExecEvent(r.tc)
 	t.tg.pidns.owner.mu.Lock()
 	t.tg.execing = nil
 	if t.killed() {
@@ -253,7 +254,7 @@ func (t *Task) promoteLocked() {
 
 	t.tg.leader = t
 	t.Infof("Becoming TID %d (in root PID namespace)", t.tg.pidns.owner.Root.tids[t])
-	t.updateLogPrefixLocked()
+	t.updateInfoLocked()
 	// Reap the original leader. If it has a tracer, detach it instead of
 	// waiting for it to acknowledge the original leader's death.
 	oldLeader.exitParentNotified = true
diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index 535f03e50..435761e5a 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -236,6 +236,7 @@ func (*runExit) execute(t *Task) taskRunState {
 type runExitMain struct{}
 
 func (*runExitMain) execute(t *Task) taskRunState {
+	t.traceExitEvent()
 	lastExiter := t.exitThreadGroup()
 
 	// If the task has a cleartid, and the thread group wasn't killed by a
diff --git a/pkg/sentry/kernel/task_log.go b/pkg/sentry/kernel/task_log.go
index a29e9b9eb..0fb3661de 100644
--- a/pkg/sentry/kernel/task_log.go
+++ b/pkg/sentry/kernel/task_log.go
@@ -16,6 +16,7 @@ package kernel
 
 import (
 	"fmt"
+	"runtime/trace"
 	"sort"
 
 	"gvisor.dev/gvisor/pkg/log"
@@ -127,11 +128,88 @@ func (t *Task) debugDumpStack() {
 	}
 }
 
-// updateLogPrefix updates the task's cached log prefix to reflect its
-// current thread ID.
+// trace definitions.
+//
+// Note that all region names are prefixed by ':' in order to ensure that they
+// are lexically ordered before all system calls, which use the naked system
+// call name (e.g. "read") for maximum clarity.
+const (
+	traceCategory = "task"
+	runRegion     = ":run"
+	blockRegion   = ":block"
+	cpuidRegion   = ":cpuid"
+	faultRegion   = ":fault"
+)
+
+// updateInfoLocked updates the task's cached log prefix and tracing
+// information to reflect its current thread ID.
 //
 // Preconditions: The task's owning TaskSet.mu must be locked.
-func (t *Task) updateLogPrefixLocked() {
+func (t *Task) updateInfoLocked() {
 	// Use the task's TID in the root PID namespace for logging.
-	t.logPrefix.Store(fmt.Sprintf("[% 4d] ", t.tg.pidns.owner.Root.tids[t]))
+	tid := t.tg.pidns.owner.Root.tids[t]
+	t.logPrefix.Store(fmt.Sprintf("[% 4d] ", tid))
+	t.rebuildTraceContext(tid)
+}
+
+// rebuildTraceContext rebuilds the trace context.
+//
+// Precondition: the passed tid must be the tid in the root namespace.
+func (t *Task) rebuildTraceContext(tid ThreadID) {
+	// Re-initialize the trace context.
+	if t.traceTask != nil {
+		t.traceTask.End()
+	}
+
+	// Note that we define the "task type" to be the dynamic TID. This does
+	// not align perfectly with the documentation for "tasks" in the
+	// tracing package. Tasks may be assumed to be bounded by analysis
+	// tools. However, if we just use a generic "task" type here, then the
+	// "user-defined tasks" page on the tracing dashboard becomes nearly
+	// unusable, as it loads all traces from all tasks.
+	//
+	// We can assume that the number of tasks in the system is not
+	// arbitrarily large (in general it won't be, especially for cases
+	// where we're collecting a brief profile), so using the TID is a
+	// reasonable compromise in this case.
+	t.traceContext, t.traceTask = trace.NewTask(t, fmt.Sprintf("tid:%d", tid))
+}
+
+// traceCloneEvent is called when a new task is spawned.
+//
+// ntid must be the new task's ThreadID in the root namespace.
+func (t *Task) traceCloneEvent(ntid ThreadID) {
+	if !trace.IsEnabled() {
+		return
+	}
+	trace.Logf(t.traceContext, traceCategory, "spawn: %d", ntid)
+}
+
+// traceExitEvent is called when a task exits.
+func (t *Task) traceExitEvent() {
+	if !trace.IsEnabled() {
+		return
+	}
+	trace.Logf(t.traceContext, traceCategory, "exit status: 0x%x", t.exitStatus.Status())
+}
+
+// traceExecEvent is called when a task calls exec.
+func (t *Task) traceExecEvent(tc *TaskContext) {
+	if !trace.IsEnabled() {
+		return
+	}
+	d := tc.MemoryManager.Executable()
+	if d == nil {
+		trace.Logf(t.traceContext, traceCategory, "exec: << unknown >>")
+		return
+	}
+	defer d.DecRef()
+	root := t.fsContext.RootDirectory()
+	if root == nil {
+		trace.Logf(t.traceContext, traceCategory, "exec: << no root directory >>")
+		return
+	}
+	defer root.DecRef()
+	n, _ := d.FullName(root)
+	trace.Logf(t.traceContext, traceCategory, "exec: %s", n)
 }
diff --git a/pkg/sentry/kernel/task_run.go b/pkg/sentry/kernel/task_run.go
index c92266c59..d97f8c189 100644
--- a/pkg/sentry/kernel/task_run.go
+++ b/pkg/sentry/kernel/task_run.go
@@ -17,6 +17,7 @@ package kernel
 import (
 	"bytes"
 	"runtime"
+	"runtime/trace"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -205,9 +206,11 @@ func (*runApp) execute(t *Task) taskRunState {
 		t.tg.pidns.owner.mu.RUnlock()
 	}
 
+	region := trace.StartRegion(t.traceContext, runRegion)
 	t.accountTaskGoroutineEnter(TaskGoroutineRunningApp)
 	info, at, err := t.p.Switch(t.MemoryManager().AddressSpace(), t.Arch(), t.rseqCPU)
 	t.accountTaskGoroutineLeave(TaskGoroutineRunningApp)
+	region.End()
 
 	if clearSinglestep {
 		t.Arch().ClearSingleStep()
@@ -225,6 +228,7 @@ func (*runApp) execute(t *Task) taskRunState {
 
 	case platform.ErrContextSignalCPUID:
 		// Is this a CPUID instruction?
+		region := trace.StartRegion(t.traceContext, cpuidRegion)
 		expected := arch.CPUIDInstruction[:]
 		found := make([]byte, len(expected))
 		_, err := t.CopyIn(usermem.Addr(t.Arch().IP()), &found)
@@ -232,10 +236,12 @@ func (*runApp) execute(t *Task) taskRunState {
 			// Skip the cpuid instruction.
 			t.Arch().CPUIDEmulate(t)
 			t.Arch().SetIP(t.Arch().IP() + uintptr(len(expected)))
+			region.End()
 
 			// Resume execution.
 			return (*runApp)(nil)
 		}
+		region.End() // Not an actual CPUID, but required copy-in.
 
 		// The instruction at the given RIP was not a CPUID, and we
 		// fallthrough to the default signal deliver behavior below.
@@ -251,8 +257,10 @@ func (*runApp) execute(t *Task) taskRunState {
 		// an application-generated signal and we should continue execution
 		// normally.
 		if at.Any() {
+			region := trace.StartRegion(t.traceContext, faultRegion)
 			addr := usermem.Addr(info.Addr())
 			err := t.MemoryManager().HandleUserFault(t, addr, at, usermem.Addr(t.Arch().Stack()))
+			region.End()
 			if err == nil {
 				// The fault was handled appropriately.
 				// We can resume running the application.
@@ -260,6 +268,12 @@ func (*runApp) execute(t *Task) taskRunState {
 			}
 
 			// Is this a vsyscall that we need emulate?
+			//
+			// Note that we don't track vsyscalls as part of a
+			// specific trace region. This is because regions don't
+			// stack, and the actual system call will count as a
+			// region. We should be able to easily identify
+			// vsyscalls by having a <fault><syscall> pair.
 			if at.Execute {
 				if sysno, ok := t.tc.st.LookupEmulate(addr); ok {
 					return t.doVsyscall(addr, sysno)
diff --git a/pkg/sentry/kernel/task_start.go b/pkg/sentry/kernel/task_start.go
index ae6fc4025..3522a4ae5 100644
--- a/pkg/sentry/kernel/task_start.go
+++ b/pkg/sentry/kernel/task_start.go
@@ -154,10 +154,10 @@ func (ts *TaskSet) newTask(cfg *TaskConfig) (*Task, error) {
 	// Below this point, newTask is expected not to fail (there is no rollback
 	// of assignTIDsLocked or any of the following).
 
-	// Logging on t's behalf will panic if t.logPrefix hasn't been initialized.
-	// This is the earliest point at which we can do so (since t now has thread
-	// IDs).
-	t.updateLogPrefixLocked()
+	// Logging on t's behalf will panic if t.logPrefix hasn't been
+	// initialized. This is the earliest point at which we can do so
+	// (since t now has thread IDs).
+	t.updateInfoLocked()
 
 	if cfg.InheritParent != nil {
 		t.parent = cfg.InheritParent.parent
diff --git a/pkg/sentry/kernel/task_syscall.go b/pkg/sentry/kernel/task_syscall.go
index b543d536a..3180f5560 100644
--- a/pkg/sentry/kernel/task_syscall.go
+++ b/pkg/sentry/kernel/task_syscall.go
@@ -17,6 +17,7 @@ package kernel
 import (
 	"fmt"
 	"os"
+	"runtime/trace"
 	"syscall"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -160,6 +161,10 @@ func (t *Task) executeSyscall(sysno uintptr, args arch.SyscallArguments) (rval u
 		ctrl = ctrlStopAndReinvokeSyscall
 	} else {
 		fn := s.Lookup(sysno)
+		var region *trace.Region // Only non-nil if tracing == true.
+		if trace.IsEnabled() {
+			region = trace.StartRegion(t.traceContext, s.LookupName(sysno))
+		}
 		if fn != nil {
 			// Call our syscall implementation.
 			rval, ctrl, err = fn(t, args)
@@ -167,6 +172,9 @@ func (t *Task) executeSyscall(sysno uintptr, args arch.SyscallArguments) (rval u
 			// Use the missing function if not found.
 			rval, err = t.SyscallTable().Missing(t, sysno, args)
 		}
+		if region != nil {
+			region.End()
+		}
 	}
 
 	if bits.IsOn32(fe, ExternalAfterEnable) && (s.ExternalFilterAfter == nil || s.ExternalFilterAfter(t, sysno, args)) {