linux-kernel - Re: [PATCH] bcache: add REQ_FUA to avoid data lost in writeback mode

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Date:   Mon, 2 Dec 2019 19:08:59 +0800
From:   Coly Li <colyli@...e.de>
To:     kungf <wings.wyang@...il.com>
Cc:     kent.overstreet@...il.com, linux-bcache@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bcache: add REQ_FUA to avoid data lost in writeback mode

On 2019/12/2 6:24 下午, kungf wrote:
> data may lost when in the follow scene of writeback mode:
> 1. client write data1 to bcache
> 2. client fdatasync
> 3. bcache flush cache set and backing device
> if now data1 was not writed back to backing, it was only guaranteed safe in cache.
> 4.then cache writeback data1 to backing with only REQ_OP_WRITE
> So data1 was not guaranteed in non-volatile storage,  it may lost if  power interruption 
> 

Hi,

Do you encounter such problem in real work load ? With bcache journal, I
don't see the possibility of data lost with your description.

Correct me if I am wrong.

Coly Li

> Signed-off-by: kungf <wings.wyang@...il.com>
> ---
>  drivers/md/bcache/writeback.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
> index 4a40f9eadeaf..e5cecb60569e 100644
> --- a/drivers/md/bcache/writeback.c
> +++ b/drivers/md/bcache/writeback.c
> @@ -357,7 +357,7 @@ static void write_dirty(struct closure *cl)
>  	 */
>  	if (KEY_DIRTY(&w->key)) {
>  		dirty_init(w);
> -		bio_set_op_attrs(&io->bio, REQ_OP_WRITE, 0);
> +		bio_set_op_attrs(&io->bio, REQ_OP_WRITE | REQ_FUA, 0);
>  		io->bio.bi_iter.bi_sector = KEY_START(&w->key);
>  		bio_set_dev(&io->bio, io->dc->bdev);
>  		io->bio.bi_end_io	= dirty_endio;
>