On Thu, Sep 05, 2013 at 02:23:25PM +0100, Al Viro wrote:
> On Thu, Sep 05, 2013 at 02:39:11PM +0200, Miklos Szeredi wrote:
> > +static bool __has_unlinked_ancestor(struct dentry *dentry)
> > +{
> > + struct dentry *this;
> > +
> > + for (this = dentry; !IS_ROOT(this); this = this->d_parent) {
> > + int is_unhashed;
> > +
> > + /* Need exclusion wrt. check_submounts_and_drop() */
> > + spin_lock(&this->d_lock);
> > + is_unhashed = d_unhashed(this);
> > + spin_unlock(&this->d_lock);
> > +
> > + if (is_unhashed)
> > + return true;
> > + }
> > + return false;
> > +}
>
> I still don't get it; why do you need to bother with early setting of
> DCACHE_MOUNTED?
>
> You are grabbing rename_lock for write in d_set_mounted(). What kind of races
> with check for submounts are you worried about? d_walk() will rescan
> everything if something grabs rename_lock for write while it had been running,
> so just fold the "have nothing in d_subdir" case of check_submounts_and_drop()
> into d_walk() and be done with that... What's the problem with such
> variant? AFAICS, all you need to care about is d_set_mounted() not getting
> between the scan for submounts and actual __d_drop() and your "finish"
> callback is called only after d_walk() having grabbed d_lock *and* rechecked
> rename_lock.
Okay, I get it. So this should work:
int d_set_mounted(struct dentry *dentry)
{
int ret = -ENOENT;
write_seqlock(&rename_lock);
if (!__has_unlinked_ancestor(dentry->d_parent)) {
spin_lock(&dentry->d_lock);
if (!d_unlinked(dentry)) {
dentry->d_flags |= DCACHE_MOUNTED;
ret = 0;
}
spin_unlock(&dentry->d_lock);
}
write_sequnlock(&rename_lock);
return ret;
}
The __has_unlinked_ancestor(dentry->d_parent) will work if dentry is a root, but
maybe it would be clearer to add that IS_ROOT explicitly?
Thanks,
Miklos
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