Re: [PATCH] block: add rationale for not using blk_mq_plug() when applicable

[Jens Axboe <axboe@kernel.dk>]

On 9/29/22 8:41 AM, Pankaj Raghav wrote:
> There are two places in the block layer at the moment where
> blk_mq_plug() helper could be used instead of directly accessing the
> plug from struct current. In both these cases, directly accessing the plug
> should not have any consequences for zoned devices.
> 
> Make the intent explicit by adding comments instead of introducing unwanted
> checks with blk_mq_plug() helper.[1]
> 
> [1] https://lore.kernel.org/linux-block/f6e54907-1035-2b2c-6387-ed178be05ccb@kernel.dk/
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Suggested-by: Jens Axboe <axboe@kernel.dk>
> ---
>  block/blk-core.c | 5 +++++
>  block/blk-mq.c   | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 203be672da52..c19d084b2a74 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -850,6 +850,11 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
>  	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
>  		return 0;
>  
> +	/* As the requests that require a zone lock are not plugged in the
> +	 * first place, directly accessing the plug instead of using
> +	 * blk_mq_plug() should not have any consequences during flushing for
> +	 * zoned devices.
> +	 */
>  	blk_flush_plug(current->plug, false);

Multi-line comments should follow the style of:

/*
 * This is a multi
 * line comment
 */

I can fix that up while applying.

-- 
Jens Axboe