block: make blk_crypto_rq_bio_prep() able to fail

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.
Suggested-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Satya Tangirala <satyat@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1617,9 +1617,11 @@ 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. */
 	rq->__sector = blk_rq_pos(rq_src);
@@ -1631,8 +1633,8 @@ 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;
 

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,
+int __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,
+/**
+ * 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;
 }
 
 /**

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,
+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;
 }
 
 /**

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);
 }