From 47b577fcc0119781ef12f6395aaec55b7d00d6ed Mon Sep 17 00:00:00 2001
From: Klaus Post <klauspost@gmail.com>
Date: Thu, 19 Aug 2021 22:21:02 +0200
Subject: [PATCH] Lock while creating buckets (#12999)

Ensure that one call will succeed and others will serialize

Example failure without code in place:
```
    bucket-policy-handlers_test.go:120: unexpected error: cmd.InsufficientWriteQuorum: Storage resources are insufficient for the write operation doz2wjqaovp5kvlrv11fyacowgcvoziszmkmzzz9nk9au946qwhci4zkane5-1/
    bucket-policy-handlers_test.go:120: unexpected error: cmd.InsufficientWriteQuorum: Storage resources are insufficient for the write operation doz2wjqaovp5kvlrv11fyacowgcvoziszmkmzzz9nk9au946qwhci4zkane5-1/
    bucket-policy-handlers_test.go:135: want 1 ok, got 0
```
---
 cmd/bucket-policy-handlers_test.go | 47 ++++++++++++++++++++++++++++++
 cmd/erasure-server-pool.go         |  9 ++++++
 2 files changed, 56 insertions(+)

diff --git a/cmd/bucket-policy-handlers_test.go b/cmd/bucket-policy-handlers_test.go
index 3614f5d73..03b8acad1 100644
--- a/cmd/bucket-policy-handlers_test.go
+++ b/cmd/bucket-policy-handlers_test.go
@@ -26,6 +26,7 @@ import (
 	"net/http/httptest"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/minio/minio/internal/auth"
@@ -93,6 +94,52 @@ func getAnonWriteOnlyObjectPolicy(bucketName, prefix string) *policy.Policy {
 	}
 }
 
+// Wrapper for calling Create Bucket and ensure we get one and only one success.
+func TestCreateBucket(t *testing.T) {
+	ExecObjectLayerAPITest(t, testCreateBucket, []string{"MakeBucketWithLocation"})
+}
+
+// testCreateBucket - Test for calling Create Bucket and ensure we get one and only one success.
+func testCreateBucket(obj ObjectLayer, instanceType, bucketName string, apiRouter http.Handler,
+	credentials auth.Credentials, t *testing.T) {
+	bucketName1 := fmt.Sprintf("%s-1", bucketName)
+
+	const n = 100
+	var start = make(chan struct{})
+	var ok, errs int
+	var wg sync.WaitGroup
+	var mu sync.Mutex
+	wg.Add(n)
+	for i := 0; i < n; i++ {
+		go func() {
+			defer wg.Done()
+			// Sync start.
+			<-start
+			if err := obj.MakeBucketWithLocation(GlobalContext, bucketName1, BucketOptions{}); err != nil {
+				if _, ok := err.(BucketExists); !ok {
+					t.Logf("unexpected error: %T: %v", err, err)
+					return
+				}
+				mu.Lock()
+				errs++
+				mu.Unlock()
+				return
+			}
+			mu.Lock()
+			ok++
+			mu.Unlock()
+		}()
+	}
+	close(start)
+	wg.Wait()
+	if ok != 1 {
+		t.Fatalf("want 1 ok, got %d", ok)
+	}
+	if errs != n-1 {
+		t.Fatalf("want %d errors, got %d", n-1, errs)
+	}
+}
+
 // Wrapper for calling Put Bucket Policy HTTP handler tests for both Erasure multiple disks and single node setup.
 func TestPutBucketPolicyHandler(t *testing.T) {
 	ExecObjectLayerAPITest(t, testPutBucketPolicyHandler, []string{"PutBucketPolicy"})
diff --git a/cmd/erasure-server-pool.go b/cmd/erasure-server-pool.go
index 647b9e7d1..45cb5bd37 100644
--- a/cmd/erasure-server-pool.go
+++ b/cmd/erasure-server-pool.go
@@ -582,6 +582,15 @@ func (z *erasureServerPools) NSScanner(ctx context.Context, bf *bloomFilter, upd
 func (z *erasureServerPools) MakeBucketWithLocation(ctx context.Context, bucket string, opts BucketOptions) error {
 	g := errgroup.WithNErrs(len(z.serverPools))
 
+	// Lock the bucket name before creating.
+	lk := z.NewNSLock(minioMetaTmpBucket, bucket+".lck")
+	lkctx, err := lk.GetLock(ctx, globalOperationTimeout)
+	if err != nil {
+		return err
+	}
+	ctx = lkctx.Context()
+	defer lk.Unlock(lkctx.Cancel)
+
 	// Create buckets in parallel across all sets.
 	for index := range z.serverPools {
 		index := index