Allow UploadCompleter and FileUploader to coexist (#42918)

Closes #33099

lib/events/filesessions/fileasync.go

@@ -380,7 +380,7 @@ func (u *upload) removeFiles() error {
 	return trace.NewAggregate(errs...)
 }
 
-func (u *Uploader) startUpload(ctx context.Context, fileName string) error {
+func (u *Uploader) startUpload(ctx context.Context, fileName string) (err error) {
 	sessionID, err := sessionIDFromPath(fileName)
 	if err != nil {
 		return trace.Wrap(err)
@@ -417,6 +417,20 @@ func (u *Uploader) startUpload(ctx context.Context, fileName string) error {
 		}
 	}
 
+	start := time.Now()
+	if err := u.takeSemaphore(ctx); err != nil {
+		return trace.Wrap(err)
+	}
+	defer func() {
+		if err != nil {
+			_ = u.releaseSemaphore(ctx)
+		}
+	}()
+
+	if time.Since(start) > 500*time.Millisecond {
+		log.Debugf("Semaphore acquired in %v for upload %v.", time.Since(start), fileName)
+	}
+
 	// Apparently, exclusive lock can be obtained only in RDWR mode on NFS
 	sessionFile, err := os.OpenFile(sessionFilePath, os.O_RDWR, 0)
 	if err != nil {
@@ -427,7 +441,7 @@ func (u *Uploader) startUpload(ctx context.Context, fileName string) error {
 		if e := sessionFile.Close(); e != nil {
 			log.WithError(e).Warningf("Failed to close %v.", fileName)
 		}
-		return trace.WrapWithMessage(err, "could not acquire file lock for %q", sessionFilePath)
+		return trace.Wrap(err, "uploader could not acquire file lock for %q", sessionFilePath)
 	}
 
 	upload := &upload{
@@ -444,16 +458,6 @@ func (u *Uploader) startUpload(ctx context.Context, fileName string) error {
 		return trace.ConvertSystemError(err)
 	}
 
-	start := time.Now()
-	if err := u.takeSemaphore(ctx); err != nil {
-		if err := upload.Close(); err != nil {
-			log.WithError(err).Warningf("Failed to close upload.")
-		}
-		return trace.Wrap(err)
-	}
-	if time.Since(start) > 500*time.Millisecond {
-		log.Debugf("Semaphore acquired in %v for upload %v.", time.Since(start), fileName)
-	}
 	u.wg.Add(1)
 	go func() {
 		defer u.wg.Done()

lib/events/filesessions/fileasync_chaos_test.go

@@ -112,11 +112,10 @@ func TestChaosUpload(t *testing.T) {
 	})
 	require.NoError(t, err)
 
-	scanPeriod := 3 * time.Second
 	uploader, err := NewUploader(UploaderConfig{
 		ScanDir:      scanDir,
 		CorruptedDir: corruptedDir,
-		ScanPeriod:   scanPeriod,
+		ScanPeriod:   3 * time.Second,
 		Streamer:     faultyStreamer,
 		Clock:        clockwork.NewRealClock(),
 	})

lib/events/filesessions/filestream.go

@@ -20,6 +20,7 @@ package filesessions
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -28,6 +29,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/google/uuid"
 	"github.com/gravitational/trace"
@@ -149,9 +151,43 @@ func (h *Handler) CompleteUpload(ctx context.Context, upload events.StreamUpload
 		return trace.ConvertSystemError(err)
 	}
 	unlock, err := utils.FSTryWriteLock(uploadPath)
-	if err != nil {
-		return trace.WrapWithMessage(err, "could not acquire file lock for %q", uploadPath)
+Loop:
+	for i := 0; i < 3; i++ {
+		switch {
+		case err == nil:
+			break Loop
+		case errors.Is(err, utils.ErrUnsuccessfulLockTry):
+			// If unable to lock the file, try again with some backoff
+			// to allow the UploadCompleter to finish and remove its
+			// file lock before giving up.
+			select {
+			case <-ctx.Done():
+				if err := f.Close(); err != nil {
+					h.WithError(err).Errorf("Failed to close file %q.", uploadPath)
+				}
+
+				return nil
+			case <-time.After(50 * time.Millisecond):
+				unlock, err = utils.FSTryWriteLock(uploadPath)
+				continue
+			}
+		default:
+			if err := f.Close(); err != nil {
+				h.WithError(err).Errorf("Failed to close file %q.", uploadPath)
+			}
+
+			return trace.Wrap(err, "handler could not acquire file lock for %q", uploadPath)
+		}
 	}
+
+	if unlock == nil {
+		if err := f.Close(); err != nil {
+			h.WithError(err).Errorf("Failed to close file %q.", uploadPath)
+		}
+
+		return trace.Wrap(err, "handler could not acquire file lock for %q", uploadPath)
+	}
+
 	defer func() {
 		if err := unlock(); err != nil {
 			h.WithError(err).Errorf("Failed to unlock filesystem lock.")