On Wed, 03 Dec 2014, Kevin Hao wrote:
> For vanilla kernel we don't need to invoke rcu_read_lock/unlock_bh
> explicitly to mark an RCU-bh critical section in the softirq context
> because bh is already disabled in this case. But for a rt kernel,
> the commit ("rcu: Merge RCU-bh into RCU-preempt") implements the
> RCU-bh in term of RCU-preempt. So we have to use
> rcu_read_lock/unlock_bh() to mark an RCU-bh critical section even in
> +
> +#ifdef CONFIG_PREEMPT_RT_FULL
> + rcu_read_lock_bh();
> +#endif
> +
> + npinfo = rcu_dereference_bh(skb->dev->npinfo);
> + ret = npinfo && (!list_empty(&npinfo->rx_np) || npinfo->rx_flags);
> +
> +#ifdef CONFIG_PREEMPT_RT_FULL
> + rcu_read_unlock_bh();
> +#endif
Is that not actually a bug indepedent of RT ?
without the rcu_read_lock/unlock who says that the
rcu_dereference is still valid at this point ?
I though that if bh are already disabled you still
need the read_lock. disabled bh would allow to "downgrad"
the rcu_read_lock_bh to rcu_read_lock but you still need it.
thx!
hofrat
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