Sebastian, > On 2020-04-16 17:01:43 [+0200], Uladzislau Rezki wrote: > > > > @@ -3139,10 +3136,8 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > > > > unsigned long flags; > > > > struct kfree_rcu_cpu *krcp; > > > > > > > > - local_irq_save(flags); // For safely calling this_cpu_ptr(). > > > > - krcp = this_cpu_ptr(&krc); > > > > - if (krcp->initialized) > > > > - spin_lock(&krcp->lock); > > > > + krcp = raw_cpu_ptr(&krc); > > > > + spin_lock_irqsave(&krcp->lock, flags); > > > > > It is not a good way to access to per-CPU variable. There is a race in > > your code. So, we will rework it anyway soon. To guarantee that we stay > > on the same CPU, first we disable IRQ's then we access per-CPU var and > > take a spinlock. > > What is the worst thing that can happen if a CPU migration happens > between raw_cpu_ptr() and spin_lock_irqsave() ? > You will just introduce higher rate of lock contention what we would like to get rid of. Could you please explain what is broken when you do like: <snip> local_irq_save(flags); krcp = this_cpu_ptr(&krc); spin_lock(&krcp->lock); <snip> Thanks! -- Vlad Rezki
