Re: [PATCH v2 2/3] block: make blk_crypto_rq_bio_prep() able to fail

[Satya Tangirala <satyat@google.com>]

On Tue, Sep 15, 2020 at 08:53:14PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> blk_crypto_rq_bio_prep() assumes its gfp_mask argument always includes
> __GFP_DIRECT_RECLAIM, so that the mempool_alloc() will always succeed.
> 
> However, blk_crypto_rq_bio_prep() might be called with GFP_ATOMIC via
> setup_clone() in drivers/md/dm-rq.c.
> 
> This case isn't currently reachable with a bio that actually has an
> encryption context.  However, it's fragile to rely on this.  Just make
> blk_crypto_rq_bio_prep() able to fail.
> 
> Cc: Miaohe Lin <linmiaohe@huawei.com>
> Suggested-by: Satya Tangirala <satyat@google.com>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  block/blk-core.c            |  8 +++++---
>  block/blk-crypto-internal.h | 21 ++++++++++++++++-----
>  block/blk-crypto.c          | 18 +++++++-----------
>  block/blk-mq.c              |  7 ++++++-
>  4 files changed, 34 insertions(+), 20 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ca3f0f00c9435..fbeaa49f6fe2c 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1620,8 +1620,10 @@ int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
>  		if (rq->bio) {
>  			rq->biotail->bi_next = bio;
>  			rq->biotail = bio;
> -		} else
> +		} else {
>  			rq->bio = rq->biotail = bio;
> +		}
> +		bio = NULL;
>  	}
>  
>  	/* Copy attributes of the original request to the clone request. */
> @@ -1634,8 +1636,8 @@ int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
>  	rq->nr_phys_segments = rq_src->nr_phys_segments;
>  	rq->ioprio = rq_src->ioprio;
>  
> -	if (rq->bio)
> -		blk_crypto_rq_bio_prep(rq, rq->bio, gfp_mask);
> +	if (rq->bio && blk_crypto_rq_bio_prep(rq, rq->bio, gfp_mask) < 0)
> +		goto free_and_out;
>  
>  	return 0;
>  
> diff --git a/block/blk-crypto-internal.h b/block/blk-crypto-internal.h
> index d2b0f565d83cb..0d36aae538d7b 100644
> --- a/block/blk-crypto-internal.h
> +++ b/block/blk-crypto-internal.h
> @@ -142,13 +142,24 @@ static inline void blk_crypto_free_request(struct request *rq)
>  		__blk_crypto_free_request(rq);
>  }
>  
> -void __blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> -			      gfp_t gfp_mask);
> -static inline void blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> -					  gfp_t gfp_mask)
> +int __blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> +			     gfp_t gfp_mask);
> +/**
> + * blk_crypto_rq_bio_prep - Prepare a request's crypt_ctx when its first bio
> + *			    is inserted
> + * @rq: The request to prepare
> + * @bio: The first bio being inserted into the request
> + * @gfp_mask: Memory allocation flags
> + *
> + * Return: 0 on success, -ENOMEM if out of memory.  -ENOMEM is only possible if
> + *	   @gfp_mask doesn't include %__GFP_DIRECT_RECLAIM.
> + */
> +static inline int blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> +					 gfp_t gfp_mask)
>  {
>  	if (bio_has_crypt_ctx(bio))
> -		__blk_crypto_rq_bio_prep(rq, bio, gfp_mask);
> +		return __blk_crypto_rq_bio_prep(rq, bio, gfp_mask);
> +	return 0;
>  }
>  
>  /**
> diff --git a/block/blk-crypto.c b/block/blk-crypto.c
> index a3f27a19067c9..bbe7974fd74f0 100644
> --- a/block/blk-crypto.c
> +++ b/block/blk-crypto.c
> @@ -283,20 +283,16 @@ bool __blk_crypto_bio_prep(struct bio **bio_ptr)
>  	return false;
>  }
>  
> -/**
> - * __blk_crypto_rq_bio_prep - Prepare a request's crypt_ctx when its first bio
> - *			      is inserted
> - *
> - * @rq: The request to prepare
> - * @bio: The first bio being inserted into the request
> - * @gfp_mask: gfp mask
> - */
> -void __blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> -			      gfp_t gfp_mask)
> +int __blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
> +			     gfp_t gfp_mask)
>  {
> -	if (!rq->crypt_ctx)
> +	if (!rq->crypt_ctx) {
>  		rq->crypt_ctx = mempool_alloc(bio_crypt_ctx_pool, gfp_mask);
> +		if (!rq->crypt_ctx)
> +			return -ENOMEM;
> +	}
>  	*rq->crypt_ctx = *bio->bi_crypt_context;
> +	return 0;
>  }
>  
>  /**
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index e04b759add758..9ec0e7149ae69 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1940,13 +1940,18 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
>  static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
>  		unsigned int nr_segs)
>  {
> +	int err;
> +
>  	if (bio->bi_opf & REQ_RAHEAD)
>  		rq->cmd_flags |= REQ_FAILFAST_MASK;
>  
>  	rq->__sector = bio->bi_iter.bi_sector;
>  	rq->write_hint = bio->bi_write_hint;
>  	blk_rq_bio_prep(rq, bio, nr_segs);
> -	blk_crypto_rq_bio_prep(rq, bio, GFP_NOIO);
> +
> +	/* This can't fail, since GFP_NOIO includes __GFP_DIRECT_RECLAIM. */
> +	err = blk_crypto_rq_bio_prep(rq, bio, GFP_NOIO);
> +	WARN_ON_ONCE(err);
>  
>  	blk_account_io_start(rq);
>  }
Looks good!

Reviewed-by: Satya Tangirala <satyat@google.com>

> -- 
> 2.28.0
>