Re: [PATCH 1/2] block: bio: ensure newly added bio flags don't override BVEC_POOL_IDX

[Jens Axboe <axboe@fb.com>]

On 3/21/19 6:30 AM, Johannes Thumshirn wrote:
> With the introduction of BIO_ALLOCED we've used up all available bits in
> bio::bi_flags.
> 
> Make sure no-one adds a new one and thus overrides the BVEC_POOL_IDX

Two minor things:

> diff --git a/block/bio.c b/block/bio.c
> index 4db1008309ed..8c689aed46a0 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -2126,12 +2126,20 @@ static void __init biovec_init_slabs(void)
>  	}
>  }
>  
> +static inline void bio_flag_buildtime_check(void)
> +{
> +	BUILD_BUG_ON(BIO_FLAG_LAST > BVEC_POOL_OFFSET);
> +}
> +
>  static int __init init_bio(void)
>  {
>  	bio_slab_max = 2;
>  	bio_slab_nr = 0;
>  	bio_slabs = kcalloc(bio_slab_max, sizeof(struct bio_slab),
>  			    GFP_KERNEL);
> +
> +	bio_flag_buildtime_check();
> +

Just add the BUILD_BUG_ON() here, don't put it in a function.

> +enum {
> +	BIO_SEG_VALID =	1,		/* bi_phys_segments valid */
> +	BIO_CLONED = 2,			/* doesn't own data */
> +	BIO_BOUNCED = 3,		/* bio is a bounce bio */
> +	BIO_USER_MAPPED = 4,		/* contains user pages */
> +	BIO_NULL_MAPPED = 5,		/* contains invalid user pages */
> +	BIO_QUIET = 6,			/* Make BIO Quiet */
> +	BIO_CHAIN = 7,			/* chained bio, ->bi_remaining in effect */
> +	BIO_REFFED = 8,			/* bio has elevated ->bi_cnt */
> +	BIO_THROTTLED =	9,		/* This bio has already been subjected to
> +					 * throttling rules. Don't do it again. */
> +	BIO_TRACE_COMPLETION = 10,	/* bio_endio() should trace the final completion
> +					 * of this bio. */
> +	BIO_QUEUE_ENTERED = 11,		/* can use blk_queue_enter_live() */
> +	BIO_TRACKED = 12,		/* set if bio goes through the rq_qos path */
> +	BIO_FLAG_LAST
> +};

Let's order this after the BIO_NO_PAGE_REF patch, so we can avoid
having to explicitly initialize the values.

You also haven't solved the issue of now having an extra bit, 2/2 uses
the last bit which the other patch already took...

-- 
Jens Axboe