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Date: Thu, 31 May 2018 11:51:40 +0900 From: Byungchul Park <byungchul.park@....com> To: paulmck@...ux.vnet.ibm.com Cc: jiangshanlai@...il.com, josh@...htriplett.org, rostedt@...dmis.org, mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org, kernel-team@....com, joel@...lfernandes.org Subject: Re: [RFC] rcu: Check the range of jiffies_till_xxx_fqs on setting them 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
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