linux-kernel - Re: [PATCH] bcache: add a check for the return of kzalloc()

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Date:   Fri, 8 Apr 2022 00:58:55 +0800
From:   Coly Li <colyli@...e.de>
To:     xkernel.wang@...mail.com
Cc:     linux-bcache@...r.kernel.org, kent.overstreet@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bcache: add a check for the return of kzalloc()

On 3/25/22 11:27 AM, xkernel.wang@...mail.com wrote:
> From: Xiaoke Wang <xkernel.wang@...mail.com>
>
> kzalloc() is a memory allocation function which can return NULL when
> some internal memory errors happen. So it is better to check it to
> prevent potential wrong memory access.
>
> Signed-off-by: Xiaoke Wang <xkernel.wang@...mail.com>
> ---
> Note: I just roughly handled the error and this seems to affect the
> original functionality. If this cannot fail, maybe the tag
> `__GFP_NOFAIL` should be considered.

The error handling is incorrect indeed. And IIRC there is someone else 
already fixes it properly and the patch is not upstream yet.

Thanks.


Coly Li


>   drivers/md/bcache/request.c | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 6d1de88..1dc9821 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -1107,14 +1107,16 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
>   	 * which would call closure_get(&dc->disk.cl)
>   	 */
>   	ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
> -	ddip->d = d;
> -	/* Count on the bcache device */
> -	ddip->orig_bdev = orig_bdev;
> -	ddip->start_time = start_time;
> -	ddip->bi_end_io = bio->bi_end_io;
> -	ddip->bi_private = bio->bi_private;
> -	bio->bi_end_io = detached_dev_end_io;
> -	bio->bi_private = ddip;
> +	if (ddip) {
> +		ddip->d = d;
> +		/* Count on the bcache device */
> +		ddip->orig_bdev = orig_bdev;
> +		ddip->start_time = start_time;
> +		ddip->bi_end_io = bio->bi_end_io;
> +		ddip->bi_private = bio->bi_private;
> +		bio->bi_end_io = detached_dev_end_io;
> +		bio->bi_private = ddip;
> +	}
>   
>   	if ((bio_op(bio) == REQ_OP_DISCARD) &&
>   	    !blk_queue_discard(bdev_get_queue(dc->bdev)))