Re: [RFC] rcu: Check the range of jiffies_till_xxx_fqs on setting them

[Byungchul Park <byungchul.park@lge.com>]

On 2018-05-31 11:18, Byungchul Park wrote:
> On 2018-05-29 21:01, Paul E. McKenney wrote:
> 
>> One approach would be to embed the kernel_params_ops structure inside
>> another structure containing the limits, then just have two structures.
>> Perhaps something like this already exists?  I don't see it right off,
>> but then again, I am not exactly an expert on module_param.
>>
>> Thoughts?
> 
> Unfortunately, I couldn't find it. There might be no way to verify
> range of a variable except the way I did. Could you give your opinion
> about whether I should go on it?

Like..

----->8-----
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4e96761..eb54d7d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -518,8 +518,38 @@ void rcu_all_qs(void)
  static ulong jiffies_till_next_fqs = ULONG_MAX;
  static bool rcu_kick_kthreads;

-module_param(jiffies_till_first_fqs, ulong, 0644);
-module_param(jiffies_till_next_fqs, ulong, 0644);
+static int param_set_first_fqs_jiffies(const char *val, const struct 
kernel_param *kp)
+{
+       ulong j;
+       int ret = kstrtoul(val, 0, &j);
+
+       if (!ret)
+               WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
+       return ret;
+}
+
+static int param_set_next_fqs_jiffies(const char *val, const struct 
kernel_param *kp)
+{
+       ulong j;
+       int ret = kstrtoul(val, 0, &j);
+
+       if (!ret)
+               WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
+       return ret;
+}
+
+static struct kernel_param_ops first_fqs_jiffies_ops = {
+       .set = param_set_first_fqs_jiffies,
+       .get = param_get_ulong,
+};
+
+static struct kernel_param_ops next_fqs_jiffies_ops = {
+       .set = param_set_next_fqs_jiffies,
+       .get = param_get_ulong,
+};
+
+module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, 
&jiffies_till_first_fqs, 0644);
+module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, 
&jiffies_till_next_fqs, 0644);
  module_param(rcu_kick_kthreads, bool, 0644);

  /*
@@ -2129,10 +2159,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
                 /* Handle quiescent-state forcing. */
                 first_gp_fqs = true;
                 j = jiffies_till_first_fqs;
-               if (j > HZ) {
-                       j = HZ;
-                       jiffies_till_first_fqs = HZ;
-               }
                 ret = 0;
                 for (;;) {
                         if (!ret) {
@@ -2167,13 +2193,6 @@ static int __noreturn rcu_gp_kthread(void *arg)
                                 WRITE_ONCE(rsp->gp_activity, jiffies);
                                 ret = 0; /* Force full wait till next 
FQS. */
                                 j = jiffies_till_next_fqs;
-                               if (j > HZ) {
-                                       j = HZ;
-                                       jiffies_till_next_fqs = HZ;
-                               } else if (j < 1) {
-                                       j = 1;
-                                       jiffies_till_next_fqs = 1;
-                               }
                         } else {
                                 /* Deal with stray signal. */
                                 cond_resched_tasks_rcu_qs();


-- 
Thanks,
Byungchul