On Fri, Dec 04, 2020 at 06:01:55PM +0100, Thomas Gleixner wrote:
> +void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
> +{
> + unsigned long flags;
> + int newcnt;
> +
> + WARN_ON_ONCE(in_hardirq());
> +
> + /* First entry of a task into a BH disabled section? */
> + if (!current->softirq_disable_cnt) {
> + if (preemptible()) {
> + local_lock(&softirq_ctrl.lock);
> + /* Required to meet the RCU bottomhalf requirements. */
> + rcu_read_lock();
> + } else {
> + DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
So, to be clear this adds a new constraint where we can't call
local_bh_disable() inside a preempt disabled section? I guess the rest of the
RT code chased all the new offenders :-)
> + }
> + }
> +
> + /*
> + * Track the per CPU softirq disabled state. On RT this is per CPU
> + * state to allow preemption of bottom half disabled sections.
> + */
> + newcnt = __this_cpu_add_return(softirq_ctrl.cnt, cnt);
> + /*
> + * Reflect the result in the task state to prevent recursion on the
> + * local lock and to make softirq_count() & al work.
> + */
> + current->softirq_disable_cnt = newcnt;
> +
> + if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
> + raw_local_irq_save(flags);
> + lockdep_softirqs_off(ip);
> + raw_local_irq_restore(flags);
> + }
> +}
> +EXPORT_SYMBOL(__local_bh_disable_ip);
> +
[...]
> +
> +void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
> +{
> + bool preempt_on = preemptible();
> + unsigned long flags;
> + u32 pending;
> + int curcnt;
> +
> + WARN_ON_ONCE(in_irq());
> + lockdep_assert_irqs_enabled();
> +
> + local_irq_save(flags);
> + curcnt = this_cpu_read(softirq_ctrl.cnt);
__this_cpu_read() ?
> +
> + /*
> + * If this is not reenabling soft interrupts, no point in trying to
> + * run pending ones.
> + */
> + if (curcnt != cnt)
> + goto out;
I guess you could move the local_irq_save() here?
> + pending = local_softirq_pending();
> + if (!pending || ksoftirqd_running(pending))
> + goto out;
> +
> + /*
> + * If this was called from non preemptible context, wake up the
> + * softirq daemon.
> + */
> + if (!preempt_on) {
> + wakeup_softirqd();
> + goto out;
> + }
> +
> + /*
> + * Adjust softirq count to SOFTIRQ_OFFSET which makes
> + * in_serving_softirq() become true.
> + */
> + cnt = SOFTIRQ_OFFSET;
> + __local_bh_enable(cnt, false);
> + __do_softirq();
> +
> +out:
> + __local_bh_enable(cnt, preempt_on);
> + local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL(__local_bh_enable_ip);
Thanks.
