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// Copyright (C) 2014 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package model
import (
"context"
"errors"
"fmt"
"path/filepath"
"strings"
"sync"
"time"
"github.com/prometheus/client_golang/prometheus"
"github.com/syncthing/syncthing/lib/events"
"github.com/syncthing/syncthing/lib/fs"
"github.com/syncthing/syncthing/lib/ur"
)
type Holdable interface {
Holders() string
}
func newDeadlockDetector(timeout time.Duration, evLogger events.Logger, fatal func(error)) *deadlockDetector {
return &deadlockDetector{
warnTimeout: timeout,
fatalTimeout: 10 * timeout,
lockers: make(map[string]sync.Locker),
evLogger: evLogger,
fatal: fatal,
}
}
type deadlockDetector struct {
warnTimeout, fatalTimeout time.Duration
lockers map[string]sync.Locker
evLogger events.Logger
fatal func(error)
}
func (d *deadlockDetector) Watch(name string, mut sync.Locker) {
d.lockers[name] = mut
go func() {
for {
time.Sleep(d.warnTimeout / 4)
done := make(chan struct{}, 1)
go func() {
mut.Lock()
_ = 1 // empty critical section
mut.Unlock()
done <- struct{}{}
}()
d.watchInner(name, done)
}
}()
}
func (d *deadlockDetector) watchInner(name string, done chan struct{}) {
warn := time.NewTimer(d.warnTimeout)
fatal := time.NewTimer(d.fatalTimeout)
defer func() {
warn.Stop()
fatal.Stop()
}()
select {
case <-warn.C:
failure := ur.FailureDataWithGoroutines(fmt.Sprintf("potential deadlock detected at %s (short timeout)", name))
failure.Extra["timeout"] = d.warnTimeout.String()
d.evLogger.Log(events.Failure, failure)
case <-done:
return
}
select {
case <-fatal.C:
err := fmt.Errorf("potential deadlock detected at %s (long timeout)", name)
failure := ur.FailureDataWithGoroutines(err.Error())
failure.Extra["timeout"] = d.fatalTimeout.String()
others := d.otherHolders()
failure.Extra["other-holders"] = others
d.evLogger.Log(events.Failure, failure)
d.fatal(err)
// Give it a minute to shut down gracefully, maybe shutting down
// can get out of the deadlock (or it's not really a deadlock).
time.Sleep(time.Minute)
panic(fmt.Sprintf("%v:\n%v", err, others))
case <-done:
}
}
func (d *deadlockDetector) otherHolders() string {
var b strings.Builder
for otherName, otherMut := range d.lockers {
if otherHolder, ok := otherMut.(Holdable); ok {
b.WriteString("===" + otherName + "===\n" + otherHolder.Holders() + "\n")
}
}
return b.String()
}
// inWritableDir calls fn(path), while making sure that the directory
// containing `path` is writable for the duration of the call.
func inWritableDir(fn func(string) error, targetFs fs.Filesystem, path string, ignorePerms bool) error {
dir := filepath.Dir(path)
info, err := targetFs.Stat(dir)
if err != nil {
return err
}
if !info.IsDir() {
return errors.New("Not a directory: " + path)
}
const permBits = fs.ModePerm | fs.ModeSetuid | fs.ModeSetgid | fs.ModeSticky
var parentErr error
if mode := info.Mode() & permBits; mode&0o200 == 0 {
// A non-writeable directory (for this user; we assume that's the
// relevant part). Temporarily change the mode so we can delete the
// file or directory inside it.
parentErr = targetFs.Chmod(dir, mode|0o700)
if parentErr != nil {
l.Debugf("Failed to make parent directory writable: %v", parentErr)
} else {
// Chmod succeeded, we should change the permissions back on the way
// out. If we fail we log the error as we have irrevocably messed up
// at this point. :( (The operation we were called to wrap has
// succeeded or failed on its own so returning an error to the
// caller is inappropriate.)
defer func() {
if err := targetFs.Chmod(dir, mode); err != nil && !fs.IsNotExist(err) {
logFn := l.Warnln
if ignorePerms {
logFn = l.Debugln
}
logFn("Failed to restore directory permissions after gaining write access:", err)
}
}()
}
}
err = fn(path)
if fs.IsPermission(err) && parentErr != nil {
err = fmt.Errorf("error after failing to make parent directory writable: %w", err)
}
return err
}
// addTimeUntilCancelled adds time to the counter for the duration of the
// Context. We do this piecemeal so that polling the counter during a long
// operation shows a relevant value, instead of the counter just increasing
// by a large amount at the end of the operation.
func addTimeUntilCancelled(ctx context.Context, counter prometheus.Counter) {
t0 := time.Now()
defer func() {
counter.Add(time.Since(t0).Seconds())
}()
ticker := time.NewTicker(time.Second)
defer ticker.Stop()
for {
select {
case t := <-ticker.C:
counter.Add(t.Sub(t0).Seconds())
t0 = t
case <-ctx.Done():
return
}
}
}
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