linux-kernel - Re: [PATCH] btrfs: Fix csum_tree_block to avoid tripping on -Werror=array-bounds

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Message-ID: <871f146c-2fd8-4322-2288-4be90c0baf8a@kylinos.cn>
Date:   Mon, 29 May 2023 11:28:59 +0800
From:   pengfuyuan <pengfuyuan@...inos.cn>
To:     dsterba@...e.cz
Cc:     Qu Wenruo <quwenruo.btrfs@....com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Fix csum_tree_block to avoid tripping on
 -Werror=array-bounds


On 2023/5/26 22:35, David Sterba wrote:
> On Tue, May 23, 2023 at 09:32:12PM +0200, David Sterba wrote:
>> On Tue, May 23, 2023 at 03:33:22PM +0800, Qu Wenruo wrote:
>>> On 2023/5/23 15:09, pengfuyuan wrote:
>>> Although even with such change, I'm still not sure if it's any better or
>>> worse, as most of the calculation can still be bulky.
>> Yeah I think the calculations would have to be conditional or keeping
>> some state. I'd like to keep the structure of the first page and the
>> rest.
>>
>> Possible ways is to add extra condition
>>
>> 	for (i = 1; i < num_pages && i < INLINE_EXTENT_BUFFER_PAGES; i++)
> The final version is
>
> 	for (i = 1; i < num_pages && INLINE_EXTENT_BUFFER_PAGES > 1; i++)
>
> ie. 'INLINE_EXTENT_BUFFER_PAGES > 1' can be evaluated at compile time
> and result in removing the for loop completely.
>
> Pengfuyuan, can you please do a build test that it does not report the
> warning anymore? The diff is:
>
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -88,7 +88,6 @@ static void csum_tree_block(struct extent_buffer *buf, u8 *result)
>          const int first_page_part = min_t(u32, PAGE_SIZE, fs_info->nodesize);
>          SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
>          char *kaddr;
> -       int i;
>   
>          shash->tfm = fs_info->csum_shash;
>          crypto_shash_init(shash);
> @@ -96,7 +95,7 @@ static void csum_tree_block(struct extent_buffer *buf, u8 *result)
>          crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
>                              first_page_part - BTRFS_CSUM_SIZE);
>   
> -       for (i = 1; i < num_pages; i++) {
> +       for (int i = 1; i < num_pages && INLINE_EXTENT_BUFFER_PAGES > 1; i++) {
>                  kaddr = page_address(buf->pages[i]);
>                  crypto_shash_update(shash, kaddr, PAGE_SIZE);
>          }
> ---

I did a build test on the mips64 architecture, the compilation passed, 
and it no longer reported warnings.

Thank you very much and wish you a happy life.


Thanks.