ppc64: fix sys32_select race with max_fdset

arch/ppc64/kernel/sys_ppc32.c

@@ -238,8 +238,6 @@ asmlinkage long sys32_writev(u32 fd, struct iovec32 *vector, u32 count)
 	return ret;
 }
 
-
-
 static inline int get_flock(struct flock *kfl, struct flock32 *ufl)
 {
 	int err;
@@ -656,7 +654,7 @@ asmlinkage long sys32_select(int n, u32 *inp, u32 *outp, u32 *exp, u32 tvp_x)
 	char *bits;
 	unsigned long nn;
 	long timeout;
-	int ret, size;
+	int ret, size, max_fdset;
 
 	timeout = MAX_SCHEDULE_TIMEOUT;
 	if (tvp) {
@@ -679,8 +677,11 @@ asmlinkage long sys32_select(int n, u32 *inp, u32 *outp, u32 *exp, u32 tvp_x)
 	ret = -EINVAL;
 	if (n < 0)
 		goto out_nofds;
-	if (n > current->files->max_fdset)
-		n = current->files->max_fdset;
+
+	/* max_fdset can increase, so grab it once to avoid race */
+	max_fdset = current->files->max_fdset;
+	if (n > max_fdset)
+		n = max_fdset;
 
 	/*
 	 * We need 6 bitmaps (in/out/ex for both incoming and outgoing),