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Date: Fri, 15 Jul 2016 13:57:33 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Jan Kara <jack@suse.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        Konstantin Khlebnikov <koct9i@gmail.com>,
        Matthew Wilcox <willy@linux.intel.com>,
        Hugh Dickins <hughd@google.com>, stable@vger.kernel.org
Subject: Re: [PATCH] radix-tree: fix radix_tree_iter_retry() for tagged
 iterators.
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On Fri, 15 Jul 2016 13:00:40 -0600 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> 
> ...
>
> In looking at this more, I agree that your patch fixes this particular bug,
> but I think that ultimately we might want something more general.
> 
> ...
>
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -463,6 +463,9 @@ static inline struct radix_tree_node *entry_to_node(void *ptr)
>  static __always_inline void **
>  radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
>  {
> +	if (unlikely(!slot))
> +		return NULL;
> +
>  	if (flags & RADIX_TREE_ITER_TAGGED) {
>  		void *canon = slot;

I'll hang onto Andrey's
radix-tree-fix-radix_tree_iter_retry-for-tagged-iterators.patch for
now, plan to send it in to Linus Wednesdayish.  If we can get the above
settled down prior to that then I shall swap over.