[PATCH v2 2/5] static_key: cancel rate limit timer on rmmod

["Radim Krčmář" <rkrcmar@redhat.com>]

Fix a bug when we free module's memory while a timer is pending by
canceling all deferred timers from the unloaded module.

static_key_rate_limit() still can't be called more than once.

Reproducer: (host crasher)
  modprobe kvm_intel
  (sleep 1; echo quit) \
    | qemu-kvm -kernel /dev/null -monitor stdio &
  sleep 0.5
  until modprobe -rv kvm_intel 2>/dev/null; do :; done

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
I decided not to post a patch that uses __deferred_key in kernel/module init,
so these three functions might seem like an overkill.

 kernel/jump_label.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 9019f15..02d610a 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -125,6 +125,27 @@ void jump_label_rate_limit(struct static_key_deferred *key,
 }
 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 
+/* could (should?) be abstracted more */
+static void with_deferred_keys(struct static_key_deferred *entry,
+                               struct static_key_deferred *stop,
+                               void (*op)(struct static_key_deferred *))
+{
+	struct static_key_deferred *iter;
+
+	for (iter = entry; iter < stop; iter++)
+		op(iter);
+}
+
+#define with_module_deferred_keys(mod, op) \
+	with_deferred_keys(mod->deferred_keys, \
+	                   mod->deferred_keys + mod->num_deferred_keys, \
+	                   op)
+
+static void deferred_key_cancel_work(struct static_key_deferred *dkey)
+{
+	cancel_delayed_work_sync(&dkey->work);
+}
+
 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 {
 	if (entry->code <= (unsigned long)end &&
@@ -385,6 +406,7 @@ jump_label_module_notify(struct notifier_block *self, unsigned long val,
 		jump_label_unlock();
 		break;
 	case MODULE_STATE_GOING:
+		with_module_deferred_keys(mod, deferred_key_cancel_work);
 		jump_label_lock();
 		jump_label_del_module(mod);
 		jump_label_unlock();
-- 
1.8.4.2