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pool: Sampler isn't protected by mutex #221

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opened 2024-05-08 11:46:14 +00:00 by dkirillov · 2 comments
dkirillov commented 2024-05-08 11:46:14 +00:00
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Expected Behavior

Sampler is thread safe.

Current Behavior

Sometimes we get panic:

мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: 2024-05-08T06:17:58.536Z        error        middleware/policy.go:49        policy validation failed        {"request_id": "f0ac6927-2c88-45b7-ac19-0a196f950ec5", "error": "get frostfs container: read container via connection pool: no healthy client"}
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:  panic: runtime error: index out of range [-2]
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:  -> math/rand.(*rngSource).Uint64
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:  ->   math/rand/rng.go:249
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     math/rand.(*rngSource).Int63
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       math/rand/rng.go:234
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     math/rand.(*Rand).Int63
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       math/rand/rand.go:96
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     math/rand.(*Rand).Float64
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       math/rand/rand.go:207
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*sampler).Next
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/sampler.go:64
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*innerPool).connection
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2142
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*Pool).connection
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2121
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*Pool).GetContainer
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2637
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs.(*FrostFS).Container
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/frostfs.go:98
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer.(*layer).containerInfo
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/container.go:49
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer.(*layer).GetBucketInfo
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/layer.go:437
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/handler.(*handler).ResolveBucket
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/handler/util.go:82
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware.policyCheck
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware/policy.go:70
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api.NewRouter.PolicyCheck.func7.1
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:       git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware/policy.go:48
мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]:     net/http.HandlerFunc.ServeHTTP

Possible Solution

Since random generator isn't thread safe but we invoke it from multiple goroutines we must protect it with mutex .

diff --git a/pool/sampler.go b/pool/sampler.go
index f5b6635..8798222 100644
--- a/pool/sampler.go
+++ b/pool/sampler.go
@@ -1,13 +1,18 @@
 package pool
 
-import "math/rand"
+import (
+	"math/rand"
+	"sync"
+)
 
 // sampler implements weighted random number generation using Vose's Alias
 // Method (https://www.keithschwarz.com/darts-dice-coins/).
 type sampler struct {
+	mu              sync.Mutex
 	randomGenerator *rand.Rand
-	probabilities   []float64
-	alias           []int
+
+	probabilities []float64
+	alias         []int
 }
 
 // newSampler creates new sampler with a given set of probabilities using
@@ -60,8 +65,13 @@ func newSampler(probabilities []float64, source rand.Source) *sampler {
 // Next returns the next (not so) random number from sampler.
 func (g *sampler) Next() int {
 	n := len(g.alias)
+
+	g.mu.Lock()
 	i := g.randomGenerator.Intn(n)
-	if g.randomGenerator.Float64() < g.probabilities[i] {
+	f := g.randomGenerator.Float64()
+	g.mu.Unlock()
+
+	if f < g.probabilities[i] {
 		return i
 	}
 	return g.alias[i]

Steps to Reproduce (for bugs)

Run the following test several times:

func TestBug(t *testing.T) {
	probabilities := []float64{0.1, 0.2, 0.7}
	s := newSampler(probabilities, rand.NewSource(0))

	for i := 0; i < 10000; i++ {
		n := 100
		var wg sync.WaitGroup
		wg.Add(n)

		for j := 0; j < n; j++ {
			go func() {
				for k := 0; k < 10; k++ {
					s.Next()
				}
				wg.Done()
			}()
		}

		wg.Wait()
	}
}

Regression

Yes

Your Environment

  • Version used: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d
<!--- Provide a general summary of the issue in the Title above --> ## Expected Behavior [Sampler](https://git.frostfs.info/TrueCloudLab/frostfs-sdk-go/src/commit/02c936f397c7bb9e1e7ca4e71b548f4deaaa32a1/pool/sampler.go#L7) is thread safe. ## Current Behavior Sometimes we get panic: ``` мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: 2024-05-08T06:17:58.536Z error middleware/policy.go:49 policy validation failed {"request_id": "f0ac6927-2c88-45b7-ac19-0a196f950ec5", "error": "get frostfs container: read container via connection pool: no healthy client"} мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: panic: runtime error: index out of range [-2] мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: -> math/rand.(*rngSource).Uint64 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: -> math/rand/rng.go:249 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand.(*rngSource).Int63 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand/rng.go:234 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand.(*Rand).Int63 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand/rand.go:96 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand.(*Rand).Float64 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: math/rand/rand.go:207 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*sampler).Next мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/sampler.go:64 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*innerPool).connection мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2142 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*Pool).connection мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2121 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool.(*Pool).GetContainer мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d/pool/pool.go:2637 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs.(*FrostFS).Container мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/frostfs.go:98 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer.(*layer).containerInfo мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/container.go:49 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer.(*layer).GetBucketInfo мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/layer.go:437 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/handler.(*handler).ResolveBucket мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/handler/util.go:82 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware.policyCheck мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware/policy.go:70 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api.NewRouter.PolicyCheck.func7.1 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware/policy.go:48 мая 08 06:17:58 vikingrock-node2 frostfs-s3-gw[8913]: net/http.HandlerFunc.ServeHTTP ``` ## Possible Solution Since [random generator](https://git.frostfs.info/TrueCloudLab/frostfs-sdk-go/src/commit/02c936f397c7bb9e1e7ca4e71b548f4deaaa32a1/pool/sampler.go#L8) isn't thread safe but we invoke it from [multiple goroutines](https://git.frostfs.info/TrueCloudLab/frostfs-sdk-go/src/commit/02c936f397c7bb9e1e7ca4e71b548f4deaaa32a1/pool/pool.go#L2146) we must protect it with mutex . ```diff diff --git a/pool/sampler.go b/pool/sampler.go index f5b6635..8798222 100644 --- a/pool/sampler.go +++ b/pool/sampler.go @@ -1,13 +1,18 @@ package pool -import "math/rand" +import ( + "math/rand" + "sync" +) // sampler implements weighted random number generation using Vose's Alias // Method (https://www.keithschwarz.com/darts-dice-coins/). type sampler struct { + mu sync.Mutex randomGenerator *rand.Rand - probabilities []float64 - alias []int + + probabilities []float64 + alias []int } // newSampler creates new sampler with a given set of probabilities using @@ -60,8 +65,13 @@ func newSampler(probabilities []float64, source rand.Source) *sampler { // Next returns the next (not so) random number from sampler. func (g *sampler) Next() int { n := len(g.alias) + + g.mu.Lock() i := g.randomGenerator.Intn(n) - if g.randomGenerator.Float64() < g.probabilities[i] { + f := g.randomGenerator.Float64() + g.mu.Unlock() + + if f < g.probabilities[i] { return i } return g.alias[i] ``` ## Steps to Reproduce (for bugs) Run the following test several times: ```golang func TestBug(t *testing.T) { probabilities := []float64{0.1, 0.2, 0.7} s := newSampler(probabilities, rand.NewSource(0)) for i := 0; i < 10000; i++ { n := 100 var wg sync.WaitGroup wg.Add(n) for j := 0; j < n; j++ { go func() { for k := 0; k < 10; k++ { s.Next() } wg.Done() }() } wg.Wait() } } ``` ## Regression Yes ## Your Environment * Version used: git.frostfs.info/TrueCloudLab/frostfs-sdk-go@v0.0.0-20240402141532-e5040d35e99d
dkirillov added the
bug
 label 2024-05-08 11:46:14 +00:00
fyrchik commented 2024-05-08 11:49:28 +00:00
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https://pkg.go.dev/golang.org/x/exp/rand has locked source, should be enough (though we can write our own wrapper too, not a rocket science).

https://pkg.go.dev/golang.org/x/exp/rand has locked source, should be enough (though we can write our own wrapper too, not a rocket science).
fyrchik commented 2024-05-08 11:53:11 +00:00
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Refs #125

Refs #125
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Reference: TrueCloudLab/frostfs-sdk-go#221
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