Re: [PATCH 3/4] XFS: Return case-insensitive match for dentry cache

[Sunil Mushran <Sunil.Mushran@xxxxxxxxxx>]

Christoph Hellwig wrote:
> The cond_resched_lock here is not safe here, because the pointer you
> are going to dereference in list_for_each_entry might not be valid
> anymore.  This should look more like:
>
> void d_drop_negative_children(struct dentry *parent)
> {
>         struct dentry *dentry;
>
>  again:
>         spin_lock(&dcache_lock);
>         list_for_each_entry(dentry, &parent->d_subdirs, d_u.d_child) {
>                 if !(dentry->d_inode)
>                         continue;
>
>                 spin_lock(&dentry->d_lock);
>                 __d_drop(dentry);
>                 spin_unlock(&dentry->d_lock);
>
> 		if (need_resched()) {
> 			spin_unlock(&dcache_lock);
> 			cond_resched();
> 			goto again;
> 		}
> 	}
> 	spin_unlock(&dcache_lock);
> }
>   
Yes, we have been bitten by the same issue.

Instead of need_resched(), it may be better if you do:

                if (cond_resched_lock(&dcache_lock))
                        goto again;