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SubjectRe: [PATCH 3/3] VFS: close race between getcwd() and d_move()
On Fri, Nov 10, 2017 at 03:45:41PM +1100, NeilBrown wrote:
> -void __d_drop(struct dentry *dentry)
> +static void ___d_drop(struct dentry *dentry)
> {
> if (!d_unhashed(dentry)) {
> struct hlist_bl_head *b;
> @@ -486,12 +488,15 @@ void __d_drop(struct dentry *dentry)
>
> hlist_bl_lock(b);
> __hlist_bl_del(&dentry->d_hash);
> - dentry->d_hash.pprev = NULL;
> hlist_bl_unlock(b);
> /* After this call, in-progress rcu-walk path lookup will fail. */
> write_seqcount_invalidate(&dentry->d_seq);
> }
> }
> +void __d_drop(struct dentry *dentry) {
> + ___d_drop(dentry);
> + dentry->d_hash.pprev = NULL;

Umm... That reordering (unhashed vs. ->d_seq) might be a problem
on the RCU side. I'm not sure it is, we might get away with that,
actually, but I want to finish digging through the pathwalk-related
code. Cursing it for being too subtle for its own good, as usual...

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