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|
package command
import (
"context"
"errors"
"fmt"
"io"
"os"
"os/exec"
"path"
"strings"
"sync"
"syscall"
"time"
"github.com/grpc-ecosystem/go-grpc-middleware/logging/logrus/ctxlogrus"
grpcmwtags "github.com/grpc-ecosystem/go-grpc-middleware/tags"
"github.com/opentracing/opentracing-go"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
"github.com/sirupsen/logrus"
"gitlab.com/gitlab-org/gitaly/v16/internal/command/commandcounter"
"gitlab.com/gitlab-org/gitaly/v16/internal/metadata/featureflag"
"gitlab.com/gitlab-org/gitaly/v16/internal/tracing"
labkittracing "gitlab.com/gitlab-org/labkit/tracing"
)
var (
cpuSecondsTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_cpu_seconds_total",
Help: "Sum of CPU time spent by shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "mode", "git_version"},
)
realSecondsTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_real_seconds_total",
Help: "Sum of real time spent by shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "git_version"},
)
minorPageFaultsTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_minor_page_faults_total",
Help: "Sum of minor page faults performed while shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "git_version"},
)
majorPageFaultsTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_major_page_faults_total",
Help: "Sum of major page faults performed while shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "git_version"},
)
signalsReceivedTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_signals_received_total",
Help: "Sum of signals received while shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "git_version"},
)
contextSwitchesTotal = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_context_switches_total",
Help: "Sum of context switches performed while shelling out",
},
[]string{"grpc_service", "grpc_method", "cmd", "subcmd", "ctxswitchtype", "git_version"},
)
spawnTokenAcquiringSeconds = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_command_spawn_token_acquiring_seconds_total",
Help: "Sum of time spent waiting for a spawn token",
},
[]string{"grpc_service", "grpc_method", "cmd", "git_version"},
)
// exportedEnvVars contains a list of environment variables
// that are always exported to child processes on spawn
exportedEnvVars = []string{
"HOME",
"PATH",
"LD_LIBRARY_PATH",
"TZ",
// Export git tracing variables for easier debugging
"GIT_TRACE",
"GIT_TRACE_PACK_ACCESS",
"GIT_TRACE_PACKET",
"GIT_TRACE_PERFORMANCE",
"GIT_TRACE_SETUP",
// GIT_EXEC_PATH tells Git where to find its binaries. This must be exported
// especially in the case where we use bundled Git executables given that we cannot
// rely on a complete Git installation in that case.
"GIT_EXEC_PATH",
// Git HTTP proxy settings:
// https://git-scm.com/docs/git-config#git-config-httpproxy
"all_proxy",
"http_proxy",
"HTTP_PROXY",
"https_proxy",
"HTTPS_PROXY",
// libcurl settings: https://curl.haxx.se/libcurl/c/CURLOPT_NOPROXY.html
"no_proxy",
"NO_PROXY",
// We must export this variable to child processes or otherwise we end up in
// an inconsistent state, where the parent process has all feature flags
// force-enabled while the child is using the usual defaults.
featureflag.EnableAllFeatureFlagsEnvVar,
}
// envInjector is responsible for injecting environment variables required for tracing into
// the child process.
envInjector = labkittracing.NewEnvInjector()
)
const (
// maxStderrBytes is at most how many bytes will be written to stderr
maxStderrBytes = 10000 // 10kb
// maxStderrLineLength is at most how many bytes a single line will be
// written to stderr. Lines exceeding this limit should be truncated
maxStderrLineLength = 4096
)
// Command encapsulates a running exec.Cmd. The embedded exec.Cmd is
// terminated and reaped automatically when the context.Context that
// created it is canceled.
type Command struct {
reader io.Reader
writer io.WriteCloser
stderrBuffer *stderrBuffer
cmd *exec.Cmd
context context.Context
startTime time.Time
waitError error
waitOnce sync.Once
processExitedCh chan struct{}
finalizers []func(context.Context, *Command)
span opentracing.Span
metricsCmd string
metricsSubCmd string
cgroupPath string
cmdGitVersion string
}
// New creates a Command from the given executable name and arguments On success, the Command
// contains a running subprocess. When ctx is canceled the embedded process will be terminated and
// reaped automatically.
func New(ctx context.Context, nameAndArgs []string, opts ...Option) (*Command, error) {
if ctx.Done() == nil {
panic("command spawned with context without Done() channel")
}
// Don't launch the command if the context is already canceled. This matches
// Go's own CommandContext's behavior which doesn't start a command if the
// context is already canceled. We can't use it currently due to it sending a
// SIGKILL to the command when the context is canceled during execution. This is not
// fine as we don't have proper logic to recover from git crashes by for example
// cleaning stale reference locks.
//
// Without this, racy behavior will emerge as the command execution will race with the
// context cancellation. This really only helps with cases when the context is already
// canceled before calling New. Raciness still ensues if the context is canceled after
// this check. More details at: https://gitlab.com/gitlab-org/gitaly/-/issues/5021
if err := ctx.Err(); err != nil {
return nil, err
}
if len(nameAndArgs) == 0 {
panic("command spawned without name")
}
if err := checkNullArgv(nameAndArgs); err != nil {
return nil, err
}
var cfg config
for _, opt := range opts {
opt(&cfg)
}
spawnStartTime := time.Now()
putToken, err := getSpawnToken(ctx)
if err != nil {
return nil, err
}
service, method := methodFromContext(ctx)
cmdName := path.Base(nameAndArgs[0])
spawnTokenAcquiringSeconds.
WithLabelValues(service, method, cmdName, cfg.gitVersion).
Add(getSpawnTokenAcquiringSeconds(spawnStartTime))
defer putToken()
logPid := -1
defer func() {
ctxlogrus.Extract(ctx).WithFields(logrus.Fields{
"pid": logPid,
"path": nameAndArgs[0],
"args": nameAndArgs[1:],
}).Debug("spawn")
}()
var spanName string
if cfg.commandName != "" && cfg.subcommandName != "" {
spanName = fmt.Sprintf("%s-%s", cfg.commandName, cfg.subcommandName)
} else {
spanName = cmdName
}
span, ctx := tracing.StartSpanIfHasParent(
ctx,
spanName,
tracing.Tags{
"path": nameAndArgs[0],
"args": strings.Join(nameAndArgs[1:], " "),
},
)
cmd := exec.Command(nameAndArgs[0], nameAndArgs[1:]...)
command := &Command{
cmd: cmd,
startTime: time.Now(),
context: ctx,
span: span,
finalizers: cfg.finalizers,
metricsCmd: cfg.commandName,
metricsSubCmd: cfg.subcommandName,
cmdGitVersion: cfg.gitVersion,
processExitedCh: make(chan struct{}),
}
cmd.Dir = cfg.dir
// Export allowed environment variables as set in the Gitaly process.
cmd.Env = AllowedEnvironment(os.Environ())
// Append environment variables explicitly requested by the caller.
cmd.Env = append(cmd.Env, cfg.environment...)
// And finally inject environment variables required for tracing into the command.
cmd.Env = envInjector(ctx, cmd.Env)
// Start the command in its own process group (nice for signalling)
cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
// Three possible values for stdin:
// * nil - Go implicitly uses /dev/null
// * stdinSentinel - configure with cmd.StdinPipe(), allowing Write() to work
// * Another io.Reader - becomes cmd.Stdin. Write() will not work
if _, ok := cfg.stdin.(stdinSentinel); ok {
pipe, err := cmd.StdinPipe()
if err != nil {
return nil, fmt.Errorf("creating stdin pipe: %w", err)
}
command.writer = pipe
} else if cfg.stdin != nil {
cmd.Stdin = cfg.stdin
}
if cfg.stdout != nil {
// We don't assign a reader if an stdout override was passed. We assume
// output is going to be directly handled by the caller.
cmd.Stdout = cfg.stdout
} else {
pipe, err := cmd.StdoutPipe()
if err != nil {
return nil, fmt.Errorf("creating stdout pipe: %w", err)
}
command.reader = pipe
}
if cfg.stderr != nil {
cmd.Stderr = cfg.stderr
} else {
command.stderrBuffer, err = newStderrBuffer(maxStderrBytes, maxStderrLineLength, []byte("\n"))
if err != nil {
return nil, fmt.Errorf("creating stderr buffer: %w", err)
}
cmd.Stderr = command.stderrBuffer
}
if err := cmd.Start(); err != nil {
return nil, fmt.Errorf("starting process %v: %w", cmd.Args, err)
}
inFlightCommandGauge.Inc()
commandcounter.Increment()
// The goroutine below is responsible for terminating and reaping the process when ctx is
// canceled. While we must ensure that it does run when `cmd.Start()` was successful, it
// must not run before have fully set up the command. Otherwise, we may end up with racy
// access patterns when the context gets terminated early.
//
// We thus defer spawning the Goroutine.
defer func() {
go func() {
select {
case <-ctx.Done():
// If the context has been cancelled and we didn't explicitly reap
// the child process then we need to manually kill it and release
// all associated resources.
if cmd.Process.Pid > 0 {
//nolint:errcheck // TODO: do we want to report errors?
// Send SIGTERM to the process group of cmd
syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM)
}
// We do not care for any potential error code, but just want to
// make sure that the subprocess gets properly killed and processed.
_ = command.Wait()
case <-command.processExitedCh:
// Otherwise, if the process has exited via a call to `wait()`
// already then there is nothing we need to do.
}
}()
}()
if featureflag.RunCommandsInCGroup.IsEnabled(ctx) && cfg.cgroupsManager != nil {
cgroupPath, err := cfg.cgroupsManager.AddCommand(command.cmd, cfg.cgroupsAddCommandOpts...)
if err != nil {
return nil, err
}
command.cgroupPath = cgroupPath
}
logPid = cmd.Process.Pid
return command, nil
}
// Read calls Read() on the stdout pipe of the command.
func (c *Command) Read(p []byte) (int, error) {
if c.reader == nil {
panic("command has no reader")
}
return c.reader.Read(p)
}
// Write calls Write() on the stdin pipe of the command.
func (c *Command) Write(p []byte) (int, error) {
if c.writer == nil {
panic("command has no writer")
}
return c.writer.Write(p)
}
// Wait calls Wait() on the exec.Cmd instance inside the command. This
// blocks until the command has finished and reports the command exit
// status via the error return value. Use ExitStatus to get the integer
// exit status from the error returned by Wait().
//
// Wait returns a wrapped context error if the process was reaped due to
// the context being done.
func (c *Command) Wait() error {
c.waitOnce.Do(c.wait)
return c.waitError
}
// This function should never be called directly, use Wait().
func (c *Command) wait() {
defer close(c.processExitedCh)
if c.writer != nil {
// Prevent the command from blocking on waiting for stdin to be closed
c.writer.Close()
}
if c.reader != nil {
// Prevent the command from blocking on writing to its stdout.
_, _ = io.Copy(io.Discard, c.reader)
}
c.waitError = c.cmd.Wait()
// If the context is done, the process was likely terminated due to it. If so,
// we return the context error to correctly report the reason.
if c.context.Err() != nil {
// The standard library sets exit status -1 if the process was terminated by a signal,
// such as the SIGTERM sent when context is done.
if exitCode, ok := ExitStatus(c.waitError); ok && exitCode == -1 {
//nolint:gitaly-linters // We can only wrap one
c.waitError = fmt.Errorf("%s: %w", c.waitError, c.context.Err())
}
}
inFlightCommandGauge.Dec()
c.logProcessComplete()
// This is a bit out-of-place here given that the `commandcounter.Increment()` call is in
// `New()`. But in `New()`, we have to resort waiting on the context being finished until we
// would be able to decrement the number of in-flight commands. Given that in some
// cases we detach processes from their initial context such that they run in the
// background, this would cause us to take longer than necessary to decrease the wait group
// counter again. So we instead do it here to accelerate the process, even though it's less
// idiomatic.
commandcounter.Decrement()
for _, finalizer := range c.finalizers {
finalizer(c.context, c)
}
}
func (c *Command) logProcessComplete() {
exitCode := 0
if c.waitError != nil {
if exitStatus, ok := ExitStatus(c.waitError); ok {
exitCode = exitStatus
}
}
ctx := c.context
cmd := c.cmd
systemTime := cmd.ProcessState.SystemTime()
userTime := cmd.ProcessState.UserTime()
realTime := time.Since(c.startTime)
fields := logrus.Fields{
"pid": cmd.ProcessState.Pid(),
"path": cmd.Path,
"args": cmd.Args,
"command.exitCode": exitCode,
"command.system_time_ms": systemTime.Milliseconds(),
"command.user_time_ms": userTime.Milliseconds(),
"command.cpu_time_ms": systemTime.Milliseconds() + userTime.Milliseconds(),
"command.real_time_ms": realTime.Milliseconds(),
}
if c.cgroupPath != "" {
fields["command.cgroup_path"] = c.cgroupPath
}
entry := ctxlogrus.Extract(ctx).WithFields(fields)
rusage, ok := cmd.ProcessState.SysUsage().(*syscall.Rusage)
if ok {
entry = entry.WithFields(logrus.Fields{
"command.maxrss": rusage.Maxrss,
"command.inblock": rusage.Inblock,
"command.oublock": rusage.Oublock,
})
}
entry.Debug("spawn complete")
if c.stderrBuffer != nil && c.stderrBuffer.Len() > 0 {
entry.Error(c.stderrBuffer.String())
}
if stats := StatsFromContext(ctx); stats != nil {
stats.RecordSum("command.count", 1)
stats.RecordSum("command.system_time_ms", int(systemTime.Milliseconds()))
stats.RecordSum("command.user_time_ms", int(userTime.Milliseconds()))
stats.RecordSum("command.cpu_time_ms", int(systemTime.Milliseconds()+userTime.Milliseconds()))
stats.RecordSum("command.real_time_ms", int(realTime.Milliseconds()))
if ok {
stats.RecordMax("command.maxrss", int(rusage.Maxrss))
stats.RecordSum("command.inblock", int(rusage.Inblock))
stats.RecordSum("command.oublock", int(rusage.Oublock))
stats.RecordSum("command.minflt", int(rusage.Minflt))
stats.RecordSum("command.majflt", int(rusage.Majflt))
}
if c.cgroupPath != "" {
stats.RecordMetadata("command.cgroup_path", c.cgroupPath)
}
}
service, method := methodFromContext(ctx)
cmdName := path.Base(c.cmd.Path)
if c.metricsCmd != "" {
cmdName = c.metricsCmd
}
cpuSecondsTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, "system", c.cmdGitVersion).Add(systemTime.Seconds())
cpuSecondsTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, "user", c.cmdGitVersion).Add(userTime.Seconds())
realSecondsTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, c.cmdGitVersion).Add(realTime.Seconds())
if ok {
minorPageFaultsTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, c.cmdGitVersion).Add(float64(rusage.Minflt))
majorPageFaultsTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, c.cmdGitVersion).Add(float64(rusage.Majflt))
signalsReceivedTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, c.cmdGitVersion).Add(float64(rusage.Nsignals))
contextSwitchesTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, "voluntary", c.cmdGitVersion).Add(float64(rusage.Nvcsw))
contextSwitchesTotal.WithLabelValues(service, method, cmdName, c.metricsSubCmd, "nonvoluntary", c.cmdGitVersion).Add(float64(rusage.Nivcsw))
}
c.span.SetTag("pid", cmd.ProcessState.Pid())
c.span.SetTag("exit_code", exitCode)
c.span.SetTag("system_time_ms", systemTime.Milliseconds())
c.span.SetTag("user_time_ms", userTime.Milliseconds())
c.span.SetTag("real_time_ms", realTime.Milliseconds())
if ok {
c.span.SetTag("maxrss", rusage.Maxrss)
c.span.SetTag("inblock", rusage.Inblock)
c.span.SetTag("oublock", rusage.Oublock)
c.span.SetTag("minflt", rusage.Minflt)
c.span.SetTag("majflt", rusage.Majflt)
}
if c.cgroupPath != "" {
c.span.SetTag("cgroup_path", c.cgroupPath)
}
c.span.Finish()
}
// Args is an accessor for the command arguments
func (c *Command) Args() []string {
return c.cmd.Args
}
// Env is an accessor for the environment variables
func (c *Command) Env() []string {
return c.cmd.Env
}
// Pid is an accessor for the pid
func (c *Command) Pid() int {
return c.cmd.Process.Pid
}
var getSpawnTokenAcquiringSeconds = func(t time.Time) float64 {
return time.Since(t).Seconds()
}
type stdinSentinel struct{}
func (stdinSentinel) Read([]byte) (int, error) {
return 0, errors.New("stdin sentinel should not be read from")
}
// AllowedEnvironment filters the given slice of environment variables and
// returns all variables which are allowed per the variables defined above.
// This is useful for constructing a base environment in which a command can be
// run.
func AllowedEnvironment(envs []string) []string {
var filtered []string
for _, env := range envs {
for _, exportedEnv := range exportedEnvVars {
if strings.HasPrefix(env, exportedEnv+"=") {
filtered = append(filtered, env)
}
}
}
return filtered
}
// ExitStatus will return the exit-code from an error returned by Wait().
func ExitStatus(err error) (int, bool) {
exitError, ok := err.(*exec.ExitError)
if !ok {
return 0, false
}
return exitError.ExitCode(), true
}
func methodFromContext(ctx context.Context) (service string, method string) {
tags := grpcmwtags.Extract(ctx)
ctxValue := tags.Values()["grpc.request.fullMethod"]
if ctxValue == nil {
return "", ""
}
if s, ok := ctxValue.(string); ok {
// Expect: "/foo.BarService/Qux"
split := strings.Split(s, "/")
if len(split) != 3 {
return "", ""
}
return split[1], split[2]
}
return "", ""
}
// Command arguments will be passed to the exec syscall as null-terminated C strings. That means the
// arguments themselves may not contain a null byte. The go stdlib checks for null bytes but it
// returns a cryptic error. This function returns a more explicit error.
func checkNullArgv(args []string) error {
for _, arg := range args {
if strings.IndexByte(arg, 0) > -1 {
// Use %q so that the null byte gets printed as \x00
return fmt.Errorf("detected null byte in command argument %q", arg)
}
}
return nil
}
|