nvmet: fix inline bio check for bdev-ns

When handling rw commands, for inline bio case we only consider
transfer size. This works well when req->sg_cnt fits into the
req->inline_bvec, but it will result in the warning in
__bio_add_page() when req->sg_cnt > NVMET_MAX_INLINE_BVEC.

Consider an I/O size 32768 and first page is not aligned to the page
boundary, then I/O is split in following manner :-

[ 2206.256140] nvmet: sg->length 3440 sg->offset 656
[ 2206.256144] nvmet: sg->length 4096 sg->offset 0
[ 2206.256148] nvmet: sg->length 4096 sg->offset 0
[ 2206.256152] nvmet: sg->length 4096 sg->offset 0
[ 2206.256155] nvmet: sg->length 4096 sg->offset 0
[ 2206.256159] nvmet: sg->length 4096 sg->offset 0
[ 2206.256163] nvmet: sg->length 4096 sg->offset 0
[ 2206.256166] nvmet: sg->length 4096 sg->offset 0
[ 2206.256170] nvmet: sg->length 656 sg->offset 0

Now the req->transfer_size == NVMET_MAX_INLINE_DATA_LEN i.e. 32768, but
the req->sg_cnt is (9) > NVMET_MAX_INLINE_BIOVEC which is (8).
This will result in the following warning message :-

nvmet_bdev_execute_rw()
	bio_add_page()
		__bio_add_page()
			WARN_ON_ONCE(bio_full(bio, len));

This scenario is very hard to reproduce on the nvme-loop transport only
with rw commands issued with the passthru IOCTL interface from the host
application and the data buffer is allocated with the malloc() and not
the posix_memalign().

Fixes: 73383adf ("nvmet: don't split large I/Os unconditionally")
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/io-cmd-bdev.c

@@ -258,7 +258,7 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
 
 	sector = nvmet_lba_to_sect(req->ns, req->cmd->rw.slba);
 
-	if (req->transfer_len <= NVMET_MAX_INLINE_DATA_LEN) {
+	if (nvmet_use_inline_bvec(req)) {
 		bio = &req->b.inline_bio;
 		bio_init(bio, req->inline_bvec, ARRAY_SIZE(req->inline_bvec));
 	} else {

drivers/nvme/target/nvmet.h

@@ -616,4 +616,10 @@ static inline sector_t nvmet_lba_to_sect(struct nvmet_ns *ns, __le64 lba)
 	return le64_to_cpu(lba) << (ns->blksize_shift - SECTOR_SHIFT);
 }
 
+static inline bool nvmet_use_inline_bvec(struct nvmet_req *req)
+{
+	return req->transfer_len <= NVMET_MAX_INLINE_DATA_LEN &&
+	       req->sg_cnt <= NVMET_MAX_INLINE_BIOVEC;
+}
+
 #endif /* _NVMET_H */