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SubjectRe: [PATCH 2/4 v6] lib: debugobjects: add global free list and the counter
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On 2/12/18 8:25 AM, Thomas Gleixner wrote:
> On Tue, 6 Feb 2018, Yang Shi wrote:
>> + /*
>> + * Reuse objs from the global free list, they will be reinitialized
>> + * when allocating
>> + */
>> + while (obj_nr_tofree > 0 && (obj_pool_free < obj_pool_min_free)) {
>> + raw_spin_lock_irqsave(&pool_lock, flags);
>> + obj = hlist_entry(obj_to_free.first, typeof(*obj), node);
> This is racy vs. the worker thread. Assume obj_nr_tofree = 1:
>
> CPU0 CPU1
> worker
> lock(&pool_lock); while (obj_nr_tofree > 0 && ...) {
> obj = hlist_entry(obj_to_free); lock(&pool_lock);
> hlist_del(obj);
> obj_nr_tofree--;
> ...
> unlock(&pool_lock);
> obj = hlist_entry(obj_to_free);
> hlist_del(obj); <------- NULL pointer dereference
>
> Not what you want, right? The counter or the list head need to be rechecked
> after the lock is acquired.

Yes, you are right. Will fix the race in newer version.

Regards,
Yang

>
>> + hlist_del(&obj->node);
>> + obj_nr_tofree--;
>> + hlist_add_head(&obj->node, &obj_pool);
>> + obj_pool_free++;
>> + raw_spin_unlock_irqrestore(&pool_lock, flags);
>> + }
> Thanks,
>
> tglx

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