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SubjectRe: [PATCH v2 1/4] dcache: Don't take unnecessary lock in d_count update
On 04/05/2013 01:12 PM, Al Viro wrote:
>> @@ -635,22 +640,14 @@ struct dentry *dget_parent(struct dentry *dentry)
>> {
>> struct dentry *ret;
>>
>> -repeat:
>> - /*
>> - * Don't need rcu_dereference because we re-check it was correct under
>> - * the lock.
>> - */
>> rcu_read_lock();
>> - ret = dentry->d_parent;
>> - spin_lock(&ret->d_lock);
>> - if (unlikely(ret != dentry->d_parent)) {
>> - spin_unlock(&ret->d_lock);
>> - rcu_read_unlock();
>> - goto repeat;
>> - }
>> + ret = rcu_dereference(dentry->d_parent);
>> rcu_read_unlock();
>> + if (dcount_inc_cmpxchg(ret))
>> + return ret;
>> + spin_lock(&ret->d_lock);
> And WTF is going to protect your "ret" from being freed just as you'd done
> rcu_read_unlock()?

I think I had made a mistake here. I should move the rcu_read_unlock()
down to before the return statement as well as after the spin_lock().
Thank for pointing this out. I will fix that in the next version.
Anything else that needs to be fixed?

Regards,
Longman


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