fix: guard server log lumberjack with mutex (#15582)

(Hopefully) closes https://github.com/coder/internal/issues/213.

cli/agent.go

@@ -12,7 +12,6 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
 	"cloud.google.com/go/compute/metadata"
@@ -30,6 +29,7 @@ import (
 	"github.com/coder/coder/v2/agent/agentssh"
 	"github.com/coder/coder/v2/agent/reaper"
 	"github.com/coder/coder/v2/buildinfo"
+	"github.com/coder/coder/v2/cli/clilog"
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/codersdk/agentsdk"
 	"github.com/coder/serpent"
@@ -110,7 +110,7 @@ func (r *RootCmd) workspaceAgent() *serpent.Command {
 			// Spawn a reaper so that we don't accumulate a ton
 			// of zombie processes.
 			if reaper.IsInitProcess() && !noReap && isLinux {
-				logWriter := &lumberjackWriteCloseFixer{w: &lumberjack.Logger{
+				logWriter := &clilog.LumberjackWriteCloseFixer{Writer: &lumberjack.Logger{
 					Filename: filepath.Join(logDir, "coder-agent-init.log"),
 					MaxSize:  5, // MB
 					// Without this, rotated logs will never be deleted.
@@ -153,7 +153,7 @@ func (r *RootCmd) workspaceAgent() *serpent.Command {
 			// reaper.
 			go DumpHandler(ctx, "agent")
 
-			logWriter := &lumberjackWriteCloseFixer{w: &lumberjack.Logger{
+			logWriter := &clilog.LumberjackWriteCloseFixer{Writer: &lumberjack.Logger{
 				Filename: filepath.Join(logDir, "coder-agent.log"),
 				MaxSize:  5, // MB
 				// Per customer incident on November 17th, 2023, its helpful
@@ -478,33 +478,6 @@ func ServeHandler(ctx context.Context, logger slog.Logger, handler http.Handler,
 	}
 }
 
-// lumberjackWriteCloseFixer is a wrapper around an io.WriteCloser that
-// prevents writes after Close. This is necessary because lumberjack
-// re-opens the file on Write.
-type lumberjackWriteCloseFixer struct {
-	w      io.WriteCloser
-	mu     sync.Mutex // Protects following.
-	closed bool
-}
-
-func (c *lumberjackWriteCloseFixer) Close() error {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
-	c.closed = true
-	return c.w.Close()
-}
-
-func (c *lumberjackWriteCloseFixer) Write(p []byte) (int, error) {
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
-	if c.closed {
-		return 0, io.ErrClosedPipe
-	}
-	return c.w.Write(p)
-}
-
 // extractPort handles different url strings.
 // - localhost:6060
 // - http://localhost:6060

cli/clilog/clilog.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"regexp"
 	"strings"
+	"sync"
 
 	"golang.org/x/xerrors"
 	"gopkg.in/natefinch/lumberjack.v2"
@@ -111,12 +112,12 @@ func (b *Builder) Build(inv *serpent.Invocation) (log slog.Logger, closeLog func
 			sinks = append(sinks, sinkFn(inv.Stderr))
 
 		default:
-			logWriter := &lumberjack.Logger{
+			logWriter := &LumberjackWriteCloseFixer{Writer: &lumberjack.Logger{
 				Filename: loc,
 				MaxSize:  5, // MB
 				// Without this, rotated logs will never be deleted.
 				MaxBackups: 1,
-			}
+			}}
 			closers = append(closers, logWriter.Close)
 			sinks = append(sinks, sinkFn(logWriter))
 		}
@@ -210,3 +211,30 @@ func (f *debugFilterSink) Sync() {
 		sink.Sync()
 	}
 }
+
+// LumberjackWriteCloseFixer is a wrapper around an io.WriteCloser that
+// prevents writes after Close. This is necessary because lumberjack
+// re-opens the file on Write.
+type LumberjackWriteCloseFixer struct {
+	Writer io.WriteCloser
+	mu     sync.Mutex // Protects following.
+	closed bool
+}
+
+func (c *LumberjackWriteCloseFixer) Close() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.closed = true
+	return c.Writer.Close()
+}
+
+func (c *LumberjackWriteCloseFixer) Write(p []byte) (int, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.closed {
+		return 0, io.ErrClosedPipe
+	}
+	return c.Writer.Write(p)
+}