RCU is not safe enough to protect __d_lookup ?

[Rock Lee]

Hi, all:
I am studying the dcache in VFS recently . I've found that hlist of dcache is already protected by RCU in __d_lookup.Is it necessary  for the function -- d_lookup using sequence lock to protect the hlist again?
struct dentry * d_lookup(struct dentry * parent, struct qstr * name){	struct dentry * dentry = NULL;	unsigned long seq;
        do {                seq = read_seqbegin(&rename_lock);                dentry = __d_lookup(parent, name);                if (dentry)			break;	} while (read_seqretry(&rename_lock, seq));	return dentry;}
Thanks in advance--------------------------------Rock Lee
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