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

[Ming Lei <tom.leiming@gmail.com>]

On Wed, Apr 3, 2019 at 5:16 PM Johannes Thumshirn <jthumshirn@suse.de> wrote:
>
> With the introduction of BIO_NO_PAGE_REF we've used up all available bits
> in bio::bi_flags.
>
> Convert the defines of the flags to an enum and add a BUILD_BUG_ON() call
> to make sure no-one adds a new one and thus overrides the BVEC_POOL_IDX
> causing crashes.
>
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
>
> ---
> This used to be part of my bio patchset but as it's a) not clear why we
> end up calling bio_put() on the on-stack bio and b) the needed prep patch
> for the fix introduces a regression, I've decided to sent this patch out
> as it's valid on it's own.
>
> I dropped Hannes' and Christoph's R-b though, as the context changed.
> ---
>  block/bio.c               |  3 +++
>  include/linux/blk_types.h | 29 ++++++++++++++++-------------
>  2 files changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 8d516d508ae3..c2592c5d70b9 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -2218,6 +2218,9 @@ static int __init init_bio(void)
>         bio_slab_nr = 0;
>         bio_slabs = kcalloc(bio_slab_max, sizeof(struct bio_slab),
>                             GFP_KERNEL);
> +
> +       BUILD_BUG_ON(BIO_FLAG_LAST > BVEC_POOL_OFFSET);
> +
>         if (!bio_slabs)
>                 panic("bio: can't allocate bios\n");
>
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 791fee35df88..be418275763c 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -215,21 +215,24 @@ struct bio {
>  /*
>   * bio flags
>   */
> -#define BIO_NO_PAGE_REF        0       /* don't put release vec pages */
> -#define BIO_SEG_VALID  1       /* bi_phys_segments valid */
> -#define BIO_CLONED     2       /* doesn't own data */
> -#define BIO_BOUNCED    3       /* bio is a bounce bio */
> -#define BIO_USER_MAPPED 4      /* contains user pages */
> -#define BIO_NULL_MAPPED 5      /* contains invalid user pages */
> -#define BIO_QUIET      6       /* Make BIO Quiet */
> -#define BIO_CHAIN      7       /* chained bio, ->bi_remaining in effect */
> -#define BIO_REFFED     8       /* bio has elevated ->bi_cnt */
> -#define BIO_THROTTLED  9       /* This bio has already been subjected to
> +enum {
> +       BIO_NO_PAGE_REF,        /* don't put release vec pages */
> +       BIO_SEG_VALID,          /* bi_phys_segments valid */
> +       BIO_CLONED,             /* doesn't own data */
> +       BIO_BOUNCED,            /* bio is a bounce bio */
> +       BIO_USER_MAPPED,        /* contains user pages */
> +       BIO_NULL_MAPPED,        /* contains invalid user pages */
> +       BIO_QUIET,              /* Make BIO Quiet */
> +       BIO_CHAIN,              /* chained bio, ->bi_remaining in effect */
> +       BIO_REFFED,             /* bio has elevated ->bi_cnt */
> +       BIO_THROTTLED,          /* This bio has already been subjected to
>                                  * throttling rules. Don't do it again. */
> -#define BIO_TRACE_COMPLETION 10        /* bio_endio() should trace the final completion
> +       BIO_TRACE_COMPLETION,   /* bio_endio() should trace the final completion
>                                  * of this bio. */
> -#define BIO_QUEUE_ENTERED 11   /* can use blk_queue_enter_live() */
> -#define BIO_TRACKED 12         /* set if bio goes through the rq_qos path */
> +       BIO_QUEUE_ENTERED,      /* can use blk_queue_enter_live() */
> +       BIO_TRACKED,            /* set if bio goes through the rq_qos path */
> +       BIO_FLAG_LAST
> +};
>
>  /* See BVEC_POOL_OFFSET below before adding new flags */

Looks fine,

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

Thanks,
Ming Lei