[PATCH v2 1/4] dcache: Don't take unnecessary lock in d_count update
Al Viro
viro at ZenIV.linux.org.uk
Fri Apr 5 11:12:20 MDT 2013
> @@ -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()?
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