linux-kernel - Re: [PATCH] block: clear iocb->private in blkdev_bio_end_io

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Date:   Tue, 22 Feb 2022 09:43:04 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        Pavel Begunkov <asml.silence@...il.com>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH] block: clear iocb->private in blkdev_bio_end_io_async()

On Fri, Feb 11, 2022 at 10:01:36AM +0100, Stefano Garzarella wrote:
> iocb_bio_iopoll() expects iocb->private to be cleared before
> releasing the bio.
> 
> We already do this in blkdev_bio_end_io(), but we forgot in the

But also iomap_dio_bio_end_io().

> recently added blkdev_bio_end_io_async().
> 
> Fixes: 54a88eb838d3 ("block: add single bio async direct IO helper")
> Cc: asml.silence@...il.com
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
> I haven't seen a failure, I was just reading the code to understand iopoll,
> so IIUC we should clean iocb->private in blkdev_bio_end_io_async().
> 
> Thanks,
> Stefano
> ---
>  block/fops.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/block/fops.c b/block/fops.c
> index 4f59e0f5bf30..a18e7fbd97b8 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -289,6 +289,8 @@ static void blkdev_bio_end_io_async(struct bio *bio)
>  	struct kiocb *iocb = dio->iocb;
>  	ssize_t ret;
>  
> +	WRITE_ONCE(iocb->private, NULL);

It might cause race in case of concurrent polling on same queue without
clearing iocb->private, so looks fine:

Reviewed-by: Ming Lei <ming.lei@...hat.com>

Thanks,
Ming