gitserver: close packed-refs file in quickRevParseHead() (#4026)

CHANGELOG.md

@@ -53,6 +53,7 @@ All notable changes to Sourcegraph are documented in this file.
 - Fixed a bug where browser extension and code review integration usage stats were not being captured on the site-admin Usage Stats page.
 - Fixed an issue where in some rare cases PostgreSQL starting up slowly could incorrectly trigger a panic in the `frontend` service.
 - Fixed an issue where the management console password would incorrectly reset to a new secure one after a user account was created.
+- Fixed a bug where gitserver would leak file descriptors when performing common operations.
 - Substantially improved the performance of updating external service configurations on instances with thousands of repositories, going from e.g. several minutes to about a minute for ~20k repositories.
 - Fully resolved the search performance regression in v3.2.0, restoring performance of search back to the same levels it was before changes made in v3.2.0.
 

cmd/gitserver/server/server.go

@@ -26,7 +26,7 @@ import (
 	"syscall"
 	"time"
 
-	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/opentracing/opentracing-go"
 	"github.com/opentracing/opentracing-go/ext"
 	otlog "github.com/opentracing/opentracing-go/log"
 	"github.com/pkg/errors"
@@ -40,7 +40,7 @@ import (
 	"github.com/sourcegraph/sourcegraph/pkg/repotrackutil"
 	"github.com/sourcegraph/sourcegraph/pkg/trace"
 	"github.com/sourcegraph/sourcegraph/pkg/vcs/git"
-	log15 "gopkg.in/inconshreveable/log15.v2"
+	"gopkg.in/inconshreveable/log15.v2"
 )
 
 // tempDirName is the name used for the temporary directory under ReposDir.
@@ -1312,6 +1312,7 @@ func quickRevParseHead(dir string) (string, error) {
 	if err != nil {
 		return "", err
 	}
+	defer f.Close()
 	scanner := bufio.NewScanner(f)
 	for scanner.Scan() {
 		fields := bytes.Fields(scanner.Bytes())