On Wed, Dec 09, 2020 at 03:24:03PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>
> Running my yearly branch profiling code, it detected a 100% wrong branch
> condition in name.c for lookup_fast(). The code in question has:
>
> status = d_revalidate(dentry, nd->flags);
> if (likely(status > 0))
> return dentry;
> if (unlazy_child(nd, dentry, seq))
> return ERR_PTR(-ECHILD);
> if (unlikely(status == -ECHILD))
> /* we'd been told to redo it in non-rcu mode */
> status = d_revalidate(dentry, nd->flags);
>
> If the status of the d_revalidate() is greater than zero, then the function
> finishes. Otherwise, if it is an "unlazy_child" it returns with -ECHILD.
> After the above two checks, the status is compared to -ECHILD, as that is
> what is returned if the original d_revalidate() needed to be done in a
> non-rcu mode.
>
> Especially this path is called in a condition of:
>
> if (nd->flags & LOOKUP_RCU) {
>
> And most of the d_revalidate() functions have:
>
> if (flags & LOOKUP_RCU)
> return -ECHILD;
Umm... That depends upon the filesystem mix involved; said that, I'd rather
drop that "unlikely"...
