linux-kernel - Re: [PATCH] mm/vmalloc: fix wrong behavior in vread

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Date:   Thu, 15 Jul 2021 12:58:13 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Chen Wandun <chenwandun@...wei.com>
Cc:     akpm@...ux-foundation.org, serapheim.dimitro@...phix.com,
        urezki@...il.com, wangkefeng.wang@...wei.com,
        weiyongjun1@...wei.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hulk Robot <hulkci@...wei.com>
Subject: Re: [PATCH] mm/vmalloc: fix wrong behavior in vread

On Wed, Jul 14, 2021 at 09:59:59AM +0800, Chen Wandun wrote:
> commit f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread()
> lookups") use rb_tree instread of list to speed up lookup, but function
> __find_vmap_area is try to find a vmap_area that include target address,
> if target address is smaller than the leftmost node in vmap_area_root,
> it will return NULL, then vread will read nothing. This behavior is
> different from the primitive semantics.
> 
> The correct way is find the first vmap_are that bigger than target addr,
> that is what function find_vmap_area_exceed_addr does.
> 
> Fixes: f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread() lookups")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Chen Wandun <chenwandun@...wei.com>
> ---
>  mm/vmalloc.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d5cd52805149..47c3a551b6dc 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -787,6 +787,28 @@ unsigned long vmalloc_nr_pages(void)
>  	return atomic_long_read(&nr_vmalloc_pages);
>  }
>  
> +static struct vmap_area *find_vmap_area_exceed_addr(unsigned long addr)
> +{
> +	struct vmap_area *va = NULL;
> +	struct rb_node *n = vmap_area_root.rb_node;
> +
> +	while (n) {
> +		struct vmap_area *tmp;
> +
> +		tmp = rb_entry(n, struct vmap_area, rb_node);
> +		if (tmp->va_end > addr) {
> +			va = tmp;
> +			if (tmp->va_start <= addr)
> +				break;
> +
> +			n = n->rb_left;
> +		} else
> +			n = n->rb_right;
> +	}
> +
> +	return va;
> +}
> +
Can we combine pvm_find_va_enclose_addr() with your new function
making it as one function? The aim is to reduce copy-paste and
not create such new "find" functions.

The pvm_find_va_enclose_addr() seems does the same but only in
reverse order. So something like:

find_vmap_area_exceed_addr(bool reverse)

Thanks!

--
Vlad Rezki