linux-kernel - Re: [PATCH] fs: btrfs: Add an assertion to warn incorrct case in insert_inline

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Date:   Tue, 30 Jul 2019 18:33:49 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.cz,
        quwenruo.btrfs@....com, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: btrfs: Add an assertion to warn incorrct case in
 insert_inline_extent()

On Sat, Jul 27, 2019 at 04:51:13PM +0800, Jia-Ju Bai wrote:
> In insert_inline_extent(), the case that compressed_size > 0 
> and compressed_pages = NULL cannot occur, otherwise a null-pointer
> dereference may occur on line 215:
>      cpage = compressed_pages[i];
> 
> To warn this incorrect case, an assertion is added.
> Thank Qu Wenruo and David Sterba for good advice.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  fs/btrfs/inode.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 1af069a9a0c7..21d6e2dcc25f 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -178,6 +178,9 @@ static int insert_inline_extent(struct btrfs_trans_handle *trans,
>  	size_t cur_size = size;
>  	unsigned long offset;
>  
> +	ASSERT((compressed_size > 0 && compressed_pages) ||
> +			(compressed_size == 0 && !compressed_pages))

Thanks. I expect that the static checking tools can be instructed to
understand that the condition has been checked and is not missing in the
code below. ASSERT is conditinally a BUG() wrapper, otherwise a no-op.

Btw, it's also good to check that the code compiles, the statement is
missing semicolon.