seccomp updates for v5.12-rc1

- Fix a non-FILTER build failure for some architectures (Paul Cercueil)
 - Improve performance with correct memory barrier (wanghongzhe)
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Merge tag 'seccomp-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull seccomp updates from Kees Cook:
 "Two small seccomp updates.

  This contains a fix for a build failure that went unnoticed for many
  years, and a memory barrier correction:

   - Fix a non-FILTER build failure for some architectures (Paul
     Cercueil)

   - Improve performance with correct memory barrier (wanghongzhe)"

* tag 'seccomp-v5.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  seccomp: Improve performace by optimizing rmb()
  seccomp: Add missing return in non-void function

kernel/seccomp.c

@@ -1164,7 +1164,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 	 * Make sure that any changes to mode from another thread have
 	 * been seen after SYSCALL_WORK_SECCOMP was seen.
 	 */
-	rmb();
+	smp_rmb();
 
 	if (!sd) {
 		populate_seccomp_data(&sd_local);
@@ -1284,6 +1284,8 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 			    const bool recheck_after_trace)
 {
 	BUG();
+
+	return -1;
 }
 #endif