Messages in this thread | | | Date | Wed, 17 Feb 2016 17:02:18 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 1/2] lib/percpu-list: Per-cpu list with associated per-cpu locks |
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On Wed, Feb 17, 2016 at 10:56:10AM -0500, Waiman Long 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); } }
> I will try to shorten the name and better document the macro. This is > probably the most tricky part of the whole part.
Note that your use of _safe() here actually makes the usage in iterate_bdevs() unsafe!
Because that function relies on __iget() pinning the current position, which means that once you re-acquire the list lock, pos->next is valid.
Howveer, _safe() takes pos->next before dropping the lock, and that object is not actually pinned and can go away.
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