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Date: Wed, 18 Mar 2026 10:23:19 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Josh Law <objecting@objecting.org>
Cc: linux-kernel@vger.kernel.org, hlcj1234567@gmail.com
Subject: Re: [PATCH] lib/assoc_array: fix stale nr_leaves_on_tree after gc
Message-Id: <20260318102319.0db807e1dc3e29fd1cde68b1@linux-foundation.org>
In-Reply-To: <20260318164959.85841-1-objecting@objecting.org>
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On Wed, 18 Mar 2026 16:49:59 +0000 Josh Law <objecting@objecting.org> wrote:

> In assoc_array_gc(), assoc_array_apply_edit() publishes the new tree
> root before nr_leaves_on_tree is updated, creating a window where the
> tree is visible with a stale leaf count. Move the nr_leaves_on_tree
> assignment before assoc_array_apply_edit() so the count is consistent
> when the new root becomes visible.
> 
> ...
>
> --- a/lib/assoc_array.c
> +++ b/lib/assoc_array.c
> @@ -1711,8 +1711,8 @@ int assoc_array_gc(struct assoc_array *array,
>  
>  gc_complete:
>  	edit->set[0].to = new_root;
> -	assoc_array_apply_edit(edit);
>  	array->nr_leaves_on_tree = nr_leaves_on_tree;
> +	assoc_array_apply_edit(edit);
>  	return 0;

But assoc_array_apply_edit() alters array->nr_leaves_on_tree and now we
immediately overwrite that alteration?