Re: [RFC PATCH] block: protect bi_status with spinlock

[Keith Busch <kbusch@xxxxxxxxxx>]

On Sun, Mar 28, 2021 at 10:23:37PM -0400, Yufen Yu wrote:
>  static struct bio *__bio_chain_endio(struct bio *bio)
>  {
>  	struct bio *parent = bio->bi_private;
> +	unsigned long flags;
>  
> +	spin_lock_irqsave(&parent->bi_lock, flags);
>  	if (!parent->bi_status)
>  		parent->bi_status = bio->bi_status;
> +	spin_unlock_irqrestore(&parent->bi_lock, flags);


I don't see a spin_lock_init() on this new lock, though a spinlock seems
overkill here. If you need an atomic update, you could do:

	cmpxchg(&parent->bi_status, 0, bio->bi_status);

But I don't even think that's necessary. There really is no need to set
parent->bi_status if bio->bi_status is 0, so something like this should
be fine:

  	if (bio->bi_status && !parent->bi_status)
  		parent->bi_status = bio->bi_status;