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tsdb/agent: Fix deadlock from simultaneous GC and write (#10166)
* tsdb/agent: Fix deadlock from simultaneous GC and write This commit fixes a potential deadlock where storing in-memory series references could deadlock with a WAL GC cycle. Signed-off-by: Robert Fratto <robertfratto@gmail.com> * add missing license header Signed-off-by: Robert Fratto <robertfratto@gmail.com> * order local imports Signed-off-by: Robert Fratto <robertfratto@gmail.com> * align deadlock testing with discovery/manager_test.go method Also prevents GCs from running concurrently, which could also cause a deadlock (even though it's currently impossible for two GCs to run concurrently). Signed-off-by: Robert Fratto <robertfratto@gmail.com>
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@ -93,6 +93,8 @@ type stripeSeries struct {
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series []map[chunks.HeadSeriesRef]*memSeries
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hashes []seriesHashmap
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locks []stripeLock
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gcMut sync.Mutex
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}
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type stripeLock struct {
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@ -120,8 +122,14 @@ func newStripeSeries(stripeSize int) *stripeSeries {
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// GC garbage collects old series that have not received a sample after mint
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// and will fully delete them.
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func (s *stripeSeries) GC(mint int64) map[chunks.HeadSeriesRef]struct{} {
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deleted := map[chunks.HeadSeriesRef]struct{}{}
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// NOTE(rfratto): GC will grab two locks, one for the hash and the other for
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// series. It's not valid for any other function to grab both locks,
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// otherwise a deadlock might occur when running GC in parallel with
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// appending.
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s.gcMut.Lock()
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defer s.gcMut.Unlock()
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deleted := map[chunks.HeadSeriesRef]struct{}{}
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for hashLock := 0; hashLock < s.size; hashLock++ {
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s.locks[hashLock].Lock()
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@ -179,14 +187,17 @@ func (s *stripeSeries) Set(hash uint64, series *memSeries) {
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hashLock = hash & uint64(s.size-1)
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refLock = uint64(series.ref) & uint64(s.size-1)
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)
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s.locks[hashLock].Lock()
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defer s.locks[hashLock].Unlock()
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if hashLock != refLock {
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s.locks[refLock].Lock()
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defer s.locks[refLock].Unlock()
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}
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s.hashes[hashLock].Set(hash, series)
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// We can't hold both locks at once otherwise we might deadlock with a
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// simulatenous call to GC.
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//
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// We update s.series first because GC expects anything in s.hashes to
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// already exist in s.series.
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s.locks[refLock].Lock()
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s.series[refLock][series.ref] = series
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s.locks[refLock].Unlock()
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s.locks[hashLock].Lock()
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s.hashes[hashLock].Set(hash, series)
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s.locks[hashLock].Unlock()
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}
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76
tsdb/agent/series_test.go
Normal file
76
tsdb/agent/series_test.go
Normal file
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@ -0,0 +1,76 @@
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// Copyright 2022 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package agent
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import (
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"fmt"
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"math"
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"sync"
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"testing"
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"time"
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"github.com/stretchr/testify/require"
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"github.com/prometheus/prometheus/model/labels"
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"github.com/prometheus/prometheus/tsdb/chunks"
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)
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func TestNoDeadlock(t *testing.T) {
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const numWorkers = 1000
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var (
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wg sync.WaitGroup
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started = make(chan struct{})
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stripeSeries = newStripeSeries(3)
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)
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wg.Add(numWorkers)
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for i := 0; i < numWorkers; i++ {
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go func() {
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defer wg.Done()
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<-started
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_ = stripeSeries.GC(math.MaxInt64)
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}()
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}
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wg.Add(numWorkers)
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for i := 0; i < numWorkers; i++ {
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go func(i int) {
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defer wg.Done()
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<-started
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series := &memSeries{
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ref: chunks.HeadSeriesRef(i),
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lset: labels.FromMap(map[string]string{
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"id": fmt.Sprintf("%d", i),
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}),
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}
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stripeSeries.Set(series.lset.Hash(), series)
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}(i)
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}
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finished := make(chan struct{})
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go func() {
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wg.Wait()
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close(finished)
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}()
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close(started)
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select {
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case <-finished:
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return
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case <-time.After(15 * time.Second):
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require.FailNow(t, "deadlock detected")
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}
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}
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