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task_start.go
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task_start.go
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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package kernel
import (
"fmt"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/atomicbitops"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/sentry/inet"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/kernel/futex"
"gvisor.dev/gvisor/pkg/sentry/kernel/sched"
"gvisor.dev/gvisor/pkg/sentry/usage"
"gvisor.dev/gvisor/pkg/sentry/vfs"
)
// TaskConfig defines the configuration of a new Task (see below).
type TaskConfig struct {
// Kernel is the owning Kernel.
Kernel *Kernel
// Parent is the new task's parent. Parent may be nil.
Parent *Task
// If InheritParent is not nil, use InheritParent's parent as the new
// task's parent.
InheritParent *Task
// ThreadGroup is the ThreadGroup the new task belongs to.
ThreadGroup *ThreadGroup
// SignalMask is the new task's initial signal mask.
SignalMask linux.SignalSet
// TaskImage is the TaskImage of the new task. Ownership of the
// TaskImage is transferred to TaskSet.NewTask, whether or not it
// succeeds.
TaskImage *TaskImage
// FSContext is the FSContext of the new task. A reference must be held on
// FSContext, which is transferred to TaskSet.NewTask whether or not it
// succeeds.
FSContext *FSContext
// FDTable is the FDTableof the new task. A reference must be held on
// FDMap, which is transferred to TaskSet.NewTask whether or not it
// succeeds.
FDTable *FDTable
// Credentials is the Credentials of the new task.
Credentials *auth.Credentials
// Niceness is the niceness of the new task.
Niceness int
// NetworkNamespace is the network namespace to be used for the new task.
NetworkNamespace *inet.Namespace
// AllowedCPUMask contains the cpus that this task can run on.
AllowedCPUMask sched.CPUSet
// UTSNamespace is the UTSNamespace of the new task.
UTSNamespace *UTSNamespace
// IPCNamespace is the IPCNamespace of the new task.
IPCNamespace *IPCNamespace
// MountNamespace is the MountNamespace of the new task.
MountNamespace *vfs.MountNamespace
// RSeqAddr is a pointer to the the userspace linux.RSeq structure.
RSeqAddr hostarch.Addr
// RSeqSignature is the signature that the rseq abort IP must be signed
// with.
RSeqSignature uint32
// ContainerID is the container the new task belongs to.
ContainerID string
// InitialCgroups are the cgroups the container is initialised to.
InitialCgroups map[Cgroup]struct{}
// UserCounters is user resource counters.
UserCounters *userCounters
// SessionKeyring is the session keyring associated with the parent task.
// It may be nil.
SessionKeyring *auth.Key
}
// NewTask creates a new task defined by cfg.
//
// NewTask does not start the returned task; the caller must call Task.Start.
//
// If successful, NewTask transfers references held by cfg to the new task.
// Otherwise, NewTask releases them.
func (ts *TaskSet) NewTask(ctx context.Context, cfg *TaskConfig) (*Task, error) {
var err error
cleanup := func() {
cfg.TaskImage.release(ctx)
cfg.FSContext.DecRef(ctx)
cfg.FDTable.DecRef(ctx)
cfg.UTSNamespace.DecRef(ctx)
cfg.IPCNamespace.DecRef(ctx)
cfg.NetworkNamespace.DecRef(ctx)
if cfg.MountNamespace != nil {
cfg.MountNamespace.DecRef(ctx)
}
}
if err := cfg.UserCounters.incRLimitNProc(ctx); err != nil {
cleanup()
return nil, err
}
t, err := ts.newTask(ctx, cfg)
if err != nil {
cfg.UserCounters.decRLimitNProc()
cleanup()
return nil, err
}
return t, nil
}
// newTask is a helper for TaskSet.NewTask that only takes ownership of parts
// of cfg if it succeeds.
func (ts *TaskSet) newTask(ctx context.Context, cfg *TaskConfig) (*Task, error) {
srcT := TaskFromContext(ctx)
tg := cfg.ThreadGroup
image := cfg.TaskImage
t := &Task{
taskNode: taskNode{
tg: tg,
parent: cfg.Parent,
children: make(map[*Task]struct{}),
},
runState: (*runApp)(nil),
interruptChan: make(chan struct{}, 1),
signalMask: atomicbitops.FromUint64(uint64(cfg.SignalMask)),
signalStack: linux.SignalStack{Flags: linux.SS_DISABLE},
image: *image,
fsContext: cfg.FSContext,
fdTable: cfg.FDTable,
k: cfg.Kernel,
ptraceTracees: make(map[*Task]struct{}),
allowedCPUMask: cfg.AllowedCPUMask.Copy(),
ioUsage: &usage.IO{},
niceness: cfg.Niceness,
utsns: cfg.UTSNamespace,
ipcns: cfg.IPCNamespace,
mountNamespace: cfg.MountNamespace,
rseqCPU: -1,
rseqAddr: cfg.RSeqAddr,
rseqSignature: cfg.RSeqSignature,
futexWaiter: futex.NewWaiter(),
containerID: cfg.ContainerID,
cgroups: make(map[Cgroup]struct{}),
userCounters: cfg.UserCounters,
sessionKeyring: cfg.SessionKeyring,
}
t.netns = cfg.NetworkNamespace
t.creds.Store(cfg.Credentials)
t.endStopCond.L = &t.tg.signalHandlers.mu
t.ptraceTracer.Store((*Task)(nil))
// We don't construct t.blockingTimer until Task.run(); see that function
// for justification.
var (
cg Cgroup
charged, committed bool
)
// Reserve cgroup PIDs controller charge. This is either commited when the
// new task enters the cgroup below, or rolled back on failure.
//
// We may also get here from a non-task context (for example, when
// creating the init task, or from the exec control command). In these cases
// we skip charging the pids controller, as non-userspace task creation
// bypasses pid limits.
if srcT != nil {
var err error
if charged, cg, err = srcT.ChargeFor(t, CgroupControllerPIDs, CgroupResourcePID, 1); err != nil {
return nil, err
}
if charged {
defer func() {
if !committed {
if err := cg.Charge(t, cg.Dentry, CgroupControllerPIDs, CgroupResourcePID, -1); err != nil {
panic(fmt.Sprintf("Failed to clean up PIDs charge on task creation failure: %v", err))
}
}
// Ref from ChargeFor. Note that we need to drop this outside of
// TaskSet.mu critical sections.
cg.DecRef(ctx)
}()
}
}
// Make the new task (and possibly thread group) visible to the rest of
// the system atomically.
ts.mu.Lock()
defer ts.mu.Unlock()
tg.signalHandlers.mu.Lock()
defer tg.signalHandlers.mu.Unlock()
if tg.exiting || tg.execing != nil {
// If the caller is in the same thread group, then what we return
// doesn't matter too much since the caller will exit before it returns
// to userspace. If the caller isn't in the same thread group, then
// we're in uncharted territory and can return whatever we want.
return nil, linuxerr.EINTR
}
if err := ts.assignTIDsLocked(t); err != nil {
return nil, err
}
// 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.updateInfoLocked()
if cfg.InheritParent != nil {
t.parent = cfg.InheritParent.parent
}
if t.parent != nil {
t.parent.children[t] = struct{}{}
}
// If InitialCgroups is not nil, the new task will be placed in the
// specified cgroups. Otherwise, if srcT is not nil, the new task will
// be placed in the srcT's cgroups. If neither is specified, the new task
// will be in the root cgroups.
t.EnterInitialCgroups(srcT, cfg.InitialCgroups)
committed = true
if tg.leader == nil {
// New thread group.
tg.leader = t
if parentPG := tg.parentPG(); parentPG == nil {
tg.createSession()
} else {
// Inherit the process group and terminal.
parentPG.incRefWithParent(parentPG)
tg.processGroup = parentPG
tg.tty = t.parent.tg.tty
}
// If our parent is a child subreaper, or if it has a child
// subreaper, then this new thread group does as well.
if t.parent != nil {
tg.hasChildSubreaper = t.parent.tg.isChildSubreaper || t.parent.tg.hasChildSubreaper
}
}
tg.tasks.PushBack(t)
tg.tasksCount++
tg.liveTasks++
tg.activeTasks++
// Propagate external TaskSet stops to the new task.
t.stopCount = atomicbitops.FromInt32(ts.stopCount)
t.mu.Lock()
defer t.mu.Unlock()
t.cpu = atomicbitops.FromInt32(assignCPU(t.allowedCPUMask, ts.Root.tids[t]))
t.startTime = t.k.RealtimeClock().Now()
// As a final step, initialize the platform context. This may require
// other pieces to be initialized as the task is used the context.
t.p = cfg.Kernel.Platform.NewContext(t.AsyncContext())
return t, nil
}
// assignTIDsLocked ensures that new task t is visible in all PID namespaces in
// which it should be visible.
//
// Preconditions: ts.mu must be locked for writing.
func (ts *TaskSet) assignTIDsLocked(t *Task) error {
type allocatedTID struct {
ns *PIDNamespace
tid ThreadID
}
var allocatedTIDs []allocatedTID
var tid ThreadID
var err error
for ns := t.tg.pidns; ns != nil; ns = ns.parent {
if tid, err = ns.allocateTID(); err != nil {
break
}
if err = ns.addTask(t, tid); err != nil {
break
}
allocatedTIDs = append(allocatedTIDs, allocatedTID{ns, tid})
}
if err != nil {
// Failure. Remove the tids we already allocated in descendant
// namespaces.
for _, a := range allocatedTIDs {
a.ns.deleteTask(t)
}
return err
}
t.tg.pidWithinNS.Store(int32(t.tg.pidns.tgids[t.tg]))
return nil
}
// allocateTID returns an unused ThreadID from ns.
//
// Preconditions: ns.owner.mu must be locked for writing.
func (ns *PIDNamespace) allocateTID() (ThreadID, error) {
if ns.exiting {
// "In this case, a subsequent fork(2) into this PID namespace will
// fail with the error ENOMEM; it is not possible to create a new
// processes [sic] in a PID namespace whose init process has
// terminated." - pid_namespaces(7)
return 0, linuxerr.ENOMEM
}
tid := ns.last
for {
// Next.
tid++
if tid > TasksLimit {
tid = initTID + 1
}
// Is it available?
tidInUse := func() bool {
if _, ok := ns.tasks[tid]; ok {
return true
}
if _, ok := ns.processGroups[ProcessGroupID(tid)]; ok {
return true
}
if _, ok := ns.sessions[SessionID(tid)]; ok {
return true
}
return false
}()
if !tidInUse {
ns.last = tid
return tid, nil
}
// Did we do a full cycle?
if tid == ns.last {
// No tid available.
return 0, linuxerr.EAGAIN
}
}
}
// Start starts the task goroutine. Start must be called exactly once for each
// task returned by NewTask.
//
// 'tid' must be the task's TID in the root PID namespace and it's used for
// debugging purposes only (set as parameter to Task.run to make it visible
// in stack dumps).
func (t *Task) Start(tid ThreadID) {
// If the task was restored, it may be "starting" after having already exited.
if t.runState == nil {
return
}
t.goroutineStopped.Add(1)
t.tg.liveGoroutines.Add(1)
t.tg.pidns.owner.liveGoroutines.Add(1)
t.tg.pidns.owner.runningGoroutines.Add(1)
// Task is now running in system mode.
t.accountTaskGoroutineLeave(TaskGoroutineNonexistent)
// Use the task's TID in the root PID namespace to make it visible in stack dumps.
go t.run(uintptr(tid)) // S/R-SAFE: synchronizes with saving through stops
}