linux-kernel - Re: [PATCH v2 32/36] maple_tree: Clear up index and last setting in single entry tree

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Message-ID: <5ca5da7f-1b17-b22b-58c4-eae41443e334@bytedance.com>
Date:   Tue, 9 May 2023 20:39:16 +0800
From:   Peng Zhang <zhangpeng.00@...edance.com>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc:     maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 32/36] maple_tree: Clear up index and last setting in
 single entry tree



在 2023/5/6 01:42, Liam R. Howlett 写道:
> When there is a single entry tree (range of 0-0 pointing to an entry),
> then ensure the limit is either 0-0 or 1-oo, depending on where the user
> walks.  Ensure the correct node setting as well; either MAS_ROOT or
> MAS_NONE.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
>   lib/maple_tree.c | 21 +++++++++++----------
>   1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index f060c71965c0d..914399519cf54 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -5022,24 +5022,25 @@ void *mas_walk(struct ma_state *mas)
>   {
>   	void *entry;
>   
> +	if (mas_is_none(mas) || mas_is_paused(mas))
if (mas_is_none(mas) || mas_is_paused(mas) || mas_is_ptr(mas))
> +		mas->node = MAS_START;

Hi, Liam
There is an issue that it cannot pass the user space test program
with this patchset.
I tested it based on 47cba14ce6fc4(linux-next/master).

The reason is that mas_walk() does not handle the state that mas is
root. The root cause is that mas_start() only handles the start state,
and returns NULL for the root state. When encountering the root state,
we can reset to start so that it is handled in mas_start().

log:
BUG at check_state_handling:3076 (1)
maple_tree(0x55d6a9838ca0) flags 1, height 0 root 0x1234500
0: 0x1234500
Pass: 453406336 Run:453406337
maple: ../../../lib/test_maple_tree.c:3076: check_state_handling: 
Assertion `0' failed.
Aborted (core dumped)
>   retry:
>   	entry = mas_state_walk(mas);
> -	if (mas_is_start(mas))
> +	if (mas_is_start(mas)) {
>   		goto retry;
> -
> -	if (mas_is_ptr(mas)) {
> +	} else if (mas_is_none(mas)) {
> +		mas->index = 0;
> +		mas->last = ULONG_MAX;
> +	} else if (mas_is_ptr(mas)) {
>   		if (!mas->index) {
>   			mas->last = 0;
> -		} else {
> -			mas->index = 1;
> -			mas->last = ULONG_MAX;
> +			return entry;
>   		}
> -		return entry;
> -	}
>   
> -	if (mas_is_none(mas)) {
> -		mas->index = 0;
> +		mas->index = 1;
>   		mas->last = ULONG_MAX;
> +		mas->node = MAS_NONE;
> +		return NULL;
>   	}
>   
>   	return entry;