On Wed, Feb 17, 2016 at 12:00:40PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 17, 2016 at 08:53:18PM +1100, Dave Chinner wrote:
> > > +/**
> > > + * for_all_percpu_list_entries - iterate over all the per-cpu list with locking
> > > + * @pos: the type * to use as a loop cursor for the current .
> > > + * @next: an internal type * variable pointing to the next entry
> > > + * @pchead: an internal struct list * of percpu list head
> > > + * @pclock: an internal variable for the current per-cpu spinlock
> > > + * @head: the head of the per-cpu list
> > > + * @member: the name of the per-cpu list within the struct
> > > + */
> > > +#define for_all_percpu_list_entries(pos, next, pchead, pclock, head, member)\
> > > + { \
> > > + int cpu; \
> > > + for_each_possible_cpu (cpu) { \
> > > + typeof(*pos) *next; \
> > > + spinlock_t *pclock = per_cpu_ptr(&(head)->lock, cpu); \
> > > + struct list_head *pchead = &per_cpu_ptr(head, cpu)->list;\
> > > + spin_lock(pclock); \
> > > + list_for_each_entry_safe(pos, next, pchead, member.list)
> > > +
> > > +#define end_all_percpu_list_entries(pclock) spin_unlock(pclock); } }
> >
> > This is a bit of a landmine
>
> Yeah, that is pretty terrible. Maybe a visitor interface is advisable?
>
> visit_percpu_list_entries(struct percpu_list *head, void (*visitor)(struct list_head *pos, void *data), void *data)
> {
> int cpu;
>
> for_each_possible_cpu(cpu) {
> spinlock_t *lock = per_cpu_ptr(&head->lock, cpu);
> struct list_head *head = per_cpu_ptr(&head->list, cpu);
> struct list_head *pos, *tmp;
>
> spin_lock(lock);
> for (pos = head->next, tmp = pos->next; pos != head; pos = tmp)
> visitor(pos, data);
I thought about this - it's the same problem as the list_lru walking
functions. That is, the visitor has to be able to drop the list lock
to do blocking operations, so the lock has to be passed to the
visitor/internal loop context somehow, and the way the callers can
use it need to be documented.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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