fix: suppress benign errors when listing processes (#14660)

agent/agent.go

@@ -1676,8 +1676,7 @@ func (a *agent) manageProcessPriority(ctx context.Context, debouncer *logDebounc
 		}
 
 		score, niceErr := proc.Niceness(a.syscaller)
-		if niceErr != nil && !xerrors.Is(niceErr, os.ErrPermission) {
+		if !isBenignProcessErr(niceErr) {
-			if !isNoSuchProcessErr(niceErr) {
 			debouncer.Warn(ctx, "unable to get proc niceness",
 				slog.F("cmd", proc.Cmd()),
 				slog.F("pid", proc.PID),
@@ -1685,9 +1684,6 @@ func (a *agent) manageProcessPriority(ctx context.Context, debouncer *logDebounc
 			)
 		}
 
-			continue
-		}
-
 		// We only want processes that don't have a nice value set
 		// so we don't override user nice values.
 		// Getpriority actually returns priority for the nice value
@@ -1699,8 +1695,7 @@ func (a *agent) manageProcessPriority(ctx context.Context, debouncer *logDebounc
 
 		if niceErr == nil {
 			err := proc.SetNiceness(a.syscaller, niceness)
-			if err != nil && !xerrors.Is(err, os.ErrPermission) {
+			if !isBenignProcessErr(err) {
-				if !isNoSuchProcessErr(err) {
 				debouncer.Warn(ctx, "unable to set proc niceness",
 					slog.F("cmd", proc.Cmd()),
 					slog.F("pid", proc.PID),
@@ -1709,14 +1704,12 @@ func (a *agent) manageProcessPriority(ctx context.Context, debouncer *logDebounc
 				)
 			}
 		}
-		}
 
 		// If the oom score is valid and it's not already set and isn't a custom value set by another process then it's ok to update it.
 		if oomScore != unsetOOMScore && oomScore != proc.OOMScoreAdj && !isCustomOOMScore(agentScore, proc) {
 			oomScoreStr := strconv.Itoa(oomScore)
 			err := afero.WriteFile(a.filesystem, fmt.Sprintf("/proc/%d/oom_score_adj", proc.PID), []byte(oomScoreStr), 0o644)
-			if err != nil && !xerrors.Is(err, os.ErrPermission) {
+			if !isBenignProcessErr(err) {
-				if !isNoSuchProcessErr(err) {
 				debouncer.Warn(ctx, "unable to set oom_score_adj",
 					slog.F("cmd", proc.Cmd()),
 					slog.F("pid", proc.PID),
@@ -1725,7 +1718,6 @@ func (a *agent) manageProcessPriority(ctx context.Context, debouncer *logDebounc
 				)
 			}
 		}
-		}
 		modProcs = append(modProcs, proc)
 	}
 	return modProcs, nil
@@ -2154,6 +2146,13 @@ func (l *logDebouncer) log(ctx context.Context, level slog.Level, msg string, fi
 	l.messages[msg] = time.Now()
 }
 
+func isBenignProcessErr(err error) bool {
+	return err != nil &&
+		(xerrors.Is(err, os.ErrNotExist) ||
+			xerrors.Is(err, os.ErrPermission) ||
+			isNoSuchProcessErr(err))
+}
+
 func isNoSuchProcessErr(err error) bool {
 	return err != nil && strings.Contains(err.Error(), "no such process")
 }

agent/agentproc/proc_unix.go

@@ -45,8 +45,7 @@ func List(fs afero.Fs, syscaller Syscaller) ([]*Process, error) {
 
 		cmdline, err := afero.ReadFile(fs, filepath.Join(defaultProcDir, entry, "cmdline"))
 		if err != nil {
-			var errNo syscall.Errno
+			if isBenignError(err) {
-			if xerrors.As(err, &errNo) && errNo == syscall.EPERM {
 				continue
 			}
 			return nil, xerrors.Errorf("read cmdline: %w", err)
@@ -54,7 +53,7 @@ func List(fs afero.Fs, syscaller Syscaller) ([]*Process, error) {
 
 		oomScore, err := afero.ReadFile(fs, filepath.Join(defaultProcDir, entry, "oom_score_adj"))
 		if err != nil {
-			if xerrors.Is(err, os.ErrPermission) {
+			if isBenignError(err) {
 				continue
 			}
 
@@ -124,3 +123,12 @@ func (p *Process) Cmd() string {
 func (p *Process) cmdLine() []string {
 	return strings.Split(p.CmdLine, "\x00")
 }
+
+func isBenignError(err error) bool {
+	var errno syscall.Errno
+	if !xerrors.As(err, &errno) {
+		return false
+	}
+
+	return errno == syscall.ESRCH || errno == syscall.EPERM || xerrors.Is(err, os.ErrNotExist)
+}