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

[Jens Axboe <axboe@kernel.dk>]

On 3/21/19 8:15 AM, Jens Axboe wrote:
> 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...

Here's one way - kill BIO_SEG_VALID. We should just use
->bi_phys_segments to tell if it's valid or not. This patch uses -1 to
signify it's not.

Totally untested...

diff --git a/block/bio.c b/block/bio.c
index 71a78d9fb8b7..4bc165e7ca43 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -280,6 +280,7 @@ void bio_init(struct bio *bio, struct bio_vec *table,
 	      unsigned short max_vecs)
 {
 	memset(bio, 0, sizeof(*bio));
+	bio->bi_phys_segments = -1;
 	atomic_set(&bio->__bi_remaining, 1);
 	atomic_set(&bio->__bi_cnt, 1);
 
@@ -305,6 +306,7 @@ void bio_reset(struct bio *bio)
 	bio_uninit(bio);
 
 	memset(bio, 0, BIO_RESET_BYTES);
+	bio->bi_phys_segments = -1;
 	bio->bi_flags = flags;
 	atomic_set(&bio->__bi_remaining, 1);
 }
@@ -573,7 +575,7 @@ EXPORT_SYMBOL(bio_put);
 
 int bio_phys_segments(struct request_queue *q, struct bio *bio)
 {
-	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+	if (unlikely(bio->bi_phys_segments == -1))
 		blk_recount_segments(q, bio);
 
 	return bio->bi_phys_segments;
@@ -731,7 +733,7 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 
 	/* If we may be able to merge these biovecs, force a recount */
 	if (bio->bi_vcnt > 1 && biovec_phys_mergeable(q, bvec - 1, bvec))
-		bio_clear_flag(bio, BIO_SEG_VALID);
+		bio->bi_phys_segments = -1;
 
  done:
 	return len;
@@ -1913,10 +1915,8 @@ void bio_trim(struct bio *bio, int offset, int size)
 	if (offset == 0 && size == bio->bi_iter.bi_size)
 		return;
 
-	bio_clear_flag(bio, BIO_SEG_VALID);
-
+	bio->bi_phys_segments = -1;
 	bio_advance(bio, offset << 9);
-
 	bio->bi_iter.bi_size = size;
 
 	if (bio_integrity(bio))
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 1c9d4f0f96ea..57cea2782a76 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -343,7 +343,6 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
 	/* physical segments can be figured out during splitting */
 	res = split ? split : *bio;
 	res->bi_phys_segments = nsegs;
-	bio_set_flag(res, BIO_SEG_VALID);
 
 	if (split) {
 		/* there isn't chance to merge the splitted bio */
@@ -440,8 +439,6 @@ void blk_recount_segments(struct request_queue *q, struct bio *bio)
 	bio->bi_next = NULL;
 	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
 	bio->bi_next = nxt;
-
-	bio_set_flag(bio, BIO_SEG_VALID);
 }
 
 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
@@ -651,9 +648,9 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
 		req_set_nomerge(q, req);
 		return 0;
 	}
-	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
+	if (req->biotail->bi_phys_segments == -1)
 		blk_recount_segments(q, req->biotail);
-	if (!bio_flagged(bio, BIO_SEG_VALID))
+	if (bio->bi_phys_segments == -1)
 		blk_recount_segments(q, bio);
 
 	return ll_new_hw_segment(q, req, bio);
@@ -673,9 +670,9 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
 		req_set_nomerge(q, req);
 		return 0;
 	}
-	if (!bio_flagged(bio, BIO_SEG_VALID))
+	if (bio->bi_phys_segments == -1)
 		blk_recount_segments(q, bio);
-	if (!bio_flagged(req->bio, BIO_SEG_VALID))
+	if (req->bio->bi_phys_segments == -1)
 		blk_recount_segments(q, req->bio);
 
 	return ll_new_hw_segment(q, req, bio);
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c033bfcb209e..79eb54dcf0f9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5247,7 +5247,7 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
 		rcu_read_unlock();
 		raid_bio->bi_next = (void*)rdev;
 		bio_set_dev(align_bi, rdev->bdev);
-		bio_clear_flag(align_bi, BIO_SEG_VALID);
+		align_bi->bi_phys_segments = -1;
 
 		if (is_badblock(rdev, align_bi->bi_iter.bi_sector,
 				bio_sectors(align_bi),
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d66bf5f32610..472059e92071 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -215,7 +215,6 @@ struct bio {
 /*
  * bio flags
  */
-#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 */

-- 
Jens Axboe