[PATCH 2/4] scftorture: Reject empty workloads before starting helpers

[Joel Fernandes]

A module loaded with nthreads=0 starts its statistics task, but cleanup
skips stopping that task. Unloading the module then leaves it executing
freed module text. Reject a zero thread count before starting helpers;
negative counts still select the online CPU count.

Also, when built as a module with reschedule-only, this leaves the
selector empty because resched_cpu() is unavailable to modules. It warns
while selecting an operation, invokes no callbacks, and can nevertheless
report SUCCESS.  Reject an empty effective selector after filtering
unsupported operations.

Both failures were reproduced in a guest without the patches.

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
---
 kernel/scftorture.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/scftorture.c b/kernel/scftorture.c
index 603b2dba1536..ff9a8271a464 100644
--- a/kernel/scftorture.c
+++ b/kernel/scftorture.c
@@ -588,6 +588,12 @@ static int __init scf_torture_init(void)
 
 	scftorture_print_module_parms("Start of test");
 
+	if (!nthreads) {
+		SCFTORTOUT_ERRSTRING("nthreads must be nonzero");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
+
 	if (weight_resched <= 0 &&
 	    weight_single <= 0 && weight_single_rpc <= 0 && weight_single_wait <= 0 &&
 	    weight_many <= 0 && weight_many_wait <= 0 &&
@@ -636,6 +642,11 @@ static int __init scf_torture_init(void)
 	scf_sel_add(weight_many_wait1, SCF_PRIM_MANY, true);
 	scf_sel_add(weight_all1, SCF_PRIM_ALL, false);
 	scf_sel_add(weight_all_wait1, SCF_PRIM_ALL, true);
+	if (!scf_sel_array_len) {
+		SCFTORTOUT_ERRSTRING("no supported operations selected");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
 	scf_sel_dump();
 
 	if (onoff_interval > 0) {
-- 
2.54.0