scftorture: Add smp_call_function() memory-ordering checks

This commit adds checks for memory misordering across calls to and
returns from smp_call_function() in the case where the caller waits.
Misordering results in a splat.

Note that in contrast to smp_call_function_single(), this code does not
test memory ordering into the handler in the no-wait case because none
of the handlers would be able to free the scf_check structure without
introducing heavy synchronization to work out which was last.

[ paulmck: s/GFP_KERNEL/GFP_ATOMIC/ per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/scftorture.c

@@ -297,11 +297,13 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
 		cpus_read_lock();
 	else
 		preempt_disable();
-	switch (scfsp->scfs_prim) {
-	case SCF_PRIM_SINGLE:
+	if (scfsp->scfs_prim == SCF_PRIM_SINGLE || scfsp->scfs_wait) {
 		scfcp = kmalloc(sizeof(*scfcp), GFP_ATOMIC);
 		if (WARN_ON_ONCE(!scfcp))
 			atomic_inc(&n_alloc_errs);
+	}
+	switch (scfsp->scfs_prim) {
+	case SCF_PRIM_SINGLE:
 		cpu = torture_random(trsp) % nr_cpu_ids;
 		if (scfsp->scfs_wait)
 			scfp->n_single_wait++;
@@ -328,11 +330,6 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
 		}
 		break;
 	case SCF_PRIM_MANY:
-		if (scfsp->scfs_wait) {
-			scfcp = kmalloc(sizeof(*scfcp), GFP_ATOMIC);
-			if (WARN_ON_ONCE(!scfcp))
-				atomic_inc(&n_alloc_errs);
-		}
 		if (scfsp->scfs_wait)
 			scfp->n_many_wait++;
 		else
@@ -356,7 +353,19 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
 			scfp->n_all_wait++;
 		else
 			scfp->n_all++;
-		smp_call_function(scf_handler, NULL, scfsp->scfs_wait);
+		if (scfcp) {
+			scfcp->scfc_cpu = -1;
+			scfcp->scfc_wait = true;
+			scfcp->scfc_out = false;
+			scfcp->scfc_in = true;
+		}
+		smp_call_function(scf_handler, scfcp, scfsp->scfs_wait);
+		if (scfcp) {
+			if (WARN_ON_ONCE(!scfcp->scfc_out))
+				atomic_inc(&n_mb_out_errs);  // Leak rather than trash!
+			else
+				kfree(scfcp);
+		}
 		break;
 	}
 	if (use_cpus_read_lock)