linux-kernel - Re: [PATCH 2/2] ext4: correct the judgment of BUG in ext4_mb_normalize

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Date:   Mon, 23 May 2022 12:05:49 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yebin10@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH 2/2] ext4: correct the judgment of BUG in
 ext4_mb_normalize_request

On Sat, May 21, 2022 at 09:42:17PM +0800, Baokun Li wrote:
> When either of the "start + size <= ac->ac_o_ex.fe_logical" or
> "start > ac->ac_o_ex.fe_logical" conditions is met, it indicates
> that the fe_logical is not in the allocated range.
> In this case, it should be bug_ON.

This seems wrong, I think that this condition is testing overflow and
it's correct as it is. Or am I missing something?

-Lukas

> 
> Fixes: dfe076c106f6 ("ext4: get rid of code duplication")
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
>  fs/ext4/mballoc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 32410b79b664..d0fb57970648 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4190,7 +4190,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  	}
>  	rcu_read_unlock();
>  
> -	if (start + size <= ac->ac_o_ex.fe_logical &&
> +	if (start + size <= ac->ac_o_ex.fe_logical ||
>  			start > ac->ac_o_ex.fe_logical) {
>  		ext4_msg(ac->ac_sb, KERN_ERR,
>  			 "start %lu, size %lu, fe_logical %lu",
> -- 
> 2.31.1
>