block: never take page references for ITER_BVEC

If we pass pages through an iov_iter we always already have a reference
in the caller.  Thus remove the ITER_BVEC_FLAG_NO_REF and don't take
reference to pages by default for bvec backed iov_iters.
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -836,15 +836,6 @@ int bio_add_page(struct bio *bio, struct page *page,
 }
 EXPORT_SYMBOL(bio_add_page);
 
-static void bio_get_pages(struct bio *bio)
-{
-	struct bvec_iter_all iter_all;
-	struct bio_vec *bvec;
-
-	bio_for_each_segment_all(bvec, bio, iter_all)
-		get_page(bvec->bv_page);
-}
-
 void bio_release_pages(struct bio *bio, bool mark_dirty)
 {
 	struct bvec_iter_all iter_all;
@@ -960,11 +951,8 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 			ret = __bio_iov_iter_get_pages(bio, iter);
 	} while (!ret && iov_iter_count(iter) && !bio_full(bio));
 
-	if (iov_iter_bvec_no_ref(iter))
+	if (is_bvec)
 		bio_set_flag(bio, BIO_NO_PAGE_REF);
-	else if (is_bvec)
-		bio_get_pages(bio);
-
 	return bio->bi_vcnt ? 0 : ret;
 }
 

drivers/block/loop.c

@@ -264,20 +264,12 @@ lo_do_transfer(struct loop_device *lo, int cmd,
 	return ret;
 }
 
-static inline void loop_iov_iter_bvec(struct iov_iter *i,
-		unsigned int direction, const struct bio_vec *bvec,
-		unsigned long nr_segs, size_t count)
-{
-	iov_iter_bvec(i, direction, bvec, nr_segs, count);
-	i->type |= ITER_BVEC_FLAG_NO_REF;
-}
-
 static int lo_write_bvec(struct file *file, struct bio_vec *bvec, loff_t *ppos)
 {
 	struct iov_iter i;
 	ssize_t bw;
 
-	loop_iov_iter_bvec(&i, WRITE, bvec, 1, bvec->bv_len);
+	iov_iter_bvec(&i, WRITE, bvec, 1, bvec->bv_len);
 
 	file_start_write(file);
 	bw = vfs_iter_write(file, &i, ppos, 0);
@@ -355,7 +347,7 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
 	ssize_t len;
 
 	rq_for_each_segment(bvec, rq, iter) {
-		loop_iov_iter_bvec(&i, READ, &bvec, 1, bvec.bv_len);
+		iov_iter_bvec(&i, READ, &bvec, 1, bvec.bv_len);
 		len = vfs_iter_read(lo->lo_backing_file, &i, &pos, 0);
 		if (len < 0)
 			return len;
@@ -396,7 +388,7 @@ static int lo_read_transfer(struct loop_device *lo, struct request *rq,
 		b.bv_offset = 0;
 		b.bv_len = bvec.bv_len;
 
-		loop_iov_iter_bvec(&i, READ, &b, 1, b.bv_len);
+		iov_iter_bvec(&i, READ, &b, 1, b.bv_len);
 		len = vfs_iter_read(lo->lo_backing_file, &i, &pos, 0);
 		if (len < 0) {
 			ret = len;
@@ -563,7 +555,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	}
 	atomic_set(&cmd->ref, 2);
 
-	loop_iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));
+	iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));
 	iter.iov_offset = offset;
 
 	cmd->iocb.ki_pos = pos;

fs/io_uring.c

@@ -997,9 +997,6 @@ static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
 	iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);
 	if (offset)
 		iov_iter_advance(iter, offset);
-
-	/* don't drop a reference to these pages */
-	iter->type |= ITER_BVEC_FLAG_NO_REF;
 	return 0;
 }
 

include/linux/uio.h

@@ -19,9 +19,6 @@ struct kvec {
 };
 
 enum iter_type {
-	/* set if ITER_BVEC doesn't hold a bv_page ref */
-	ITER_BVEC_FLAG_NO_REF = 2,
-
 	/* iter types */
 	ITER_IOVEC = 4,
 	ITER_KVEC = 8,
@@ -56,7 +53,7 @@ struct iov_iter {
 
 static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 {
-	return i->type & ~(READ | WRITE | ITER_BVEC_FLAG_NO_REF);
+	return i->type & ~(READ | WRITE);
 }
 
 static inline bool iter_is_iovec(const struct iov_iter *i)
@@ -89,11 +86,6 @@ static inline unsigned char iov_iter_rw(const struct iov_iter *i)
 	return i->type & (READ | WRITE);
 }
 
-static inline bool iov_iter_bvec_no_ref(const struct iov_iter *i)
-{
-	return (i->type & ITER_BVEC_FLAG_NO_REF) != 0;
-}
-
 /*
  * Total number of bytes covered by an iovec.
  *