block: never take page references for ITER_BVEC

Cherry-pick from commit b620743077e291ae7d0debd21f50413a8c266229 upstream.

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.

[Joseph] Resolve conflicts since we don't have:
81ba6abd2bcd "block: loop: mark bvec as ITER_BVEC_FLAG_NO_REF"
7321ecbfc7cf "block: change how we get page references in bio_iov_iter_get_pages"
Reviewed-by: NMinwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

block/bio.c

@@ -933,7 +933,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	 * If this is a BVEC iter, then the pages are kernel pages. Don't
 	 * release them on IO completion, if the caller asked us to.
 	 */
-	if (is_bvec && iov_iter_bvec_no_ref(iter))
+	if (is_bvec)
 		bio_set_flag(bio, BIO_NO_PAGE_REF);
 
 	do {

fs/io_uring.c

@@ -1063,9 +1063,6 @@ 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

@@ -22,9 +22,6 @@ 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,
@@ -58,7 +55,7 @@ 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)
@@ -86,11 +83,6 @@ 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.
  *