fs: move guard_bio_eod() after bio_set_op_attrs

Commit 85a8ce6 ("block: add bio_truncate to fix guard_bio_eod")
adds bio_truncate() for handling bio EOD. However, bio_truncate()
doesn't use the passed 'op' parameter from guard_bio_eod's callers.

So bio_trunacate() may retrieve wrong 'op', and zering pages may
not be done for READ bio.

Fixes this issue by moving guard_bio_eod() after bio_set_op_attrs()
in submit_bh_wbc() so that bio_truncate() can always retrieve correct
op info.

Meantime remove the 'op' parameter from guard_bio_eod() because it isn't
used any more.

Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: linux-fsdevel@vger.kernel.org
Fixes: 85a8ce6 ("block: add bio_truncate to fix guard_bio_eod")
Signed-off-by: Ming Lei <ming.lei@redhat.com>

Fold in kerneldoc and bio_op() change.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

block/bio.c

@@ -538,6 +538,16 @@ void zero_fill_bio_iter(struct bio *bio, struct bvec_iter start)
 }
 EXPORT_SYMBOL(zero_fill_bio_iter);
 
+/**
+ * bio_truncate - truncate the bio to small size of @new_size
+ * @bio:	the bio to be truncated
+ * @new_size:	new size for truncating the bio
+ *
+ * Description:
+ *   Truncate the bio to new size of @new_size. If bio_op(bio) is
+ *   REQ_OP_READ, zero the truncated part. This function should only
+ *   be used for handling corner cases, such as bio eod.
+ */
 void bio_truncate(struct bio *bio, unsigned new_size)
 {
 	struct bio_vec bv;
@@ -548,7 +558,7 @@ void bio_truncate(struct bio *bio, unsigned new_size)
 	if (new_size >= bio->bi_iter.bi_size)
 		return;
 
-	if (bio_data_dir(bio) != READ)
+	if (bio_op(bio) != REQ_OP_READ)
 		goto exit;
 
 	bio_for_each_segment(bv, bio, iter) {

fs/buffer.c

@@ -3031,7 +3031,7 @@ static void end_bio_bh_io_sync(struct bio *bio)
  * errors, this only handles the "we need to be able to
  * do IO at the final sector" case.
  */
-void guard_bio_eod(int op, struct bio *bio)
+void guard_bio_eod(struct bio *bio)
 {
 	sector_t maxsector;
 	struct hd_struct *part;
@@ -3095,15 +3095,15 @@ static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
 	bio->bi_end_io = end_bio_bh_io_sync;
 	bio->bi_private = bh;
 
-	/* Take care of bh's that straddle the end of the device */
-	guard_bio_eod(op, bio);
-
 	if (buffer_meta(bh))
 		op_flags |= REQ_META;
 	if (buffer_prio(bh))
 		op_flags |= REQ_PRIO;
 	bio_set_op_attrs(bio, op, op_flags);
 
+	/* Take care of bh's that straddle the end of the device */
+	guard_bio_eod(bio);
+
 	if (wbc) {
 		wbc_init_bio(wbc, bio);
 		wbc_account_cgroup_owner(wbc, bh->b_page, bh->b_size);

fs/internal.h

@@ -38,7 +38,7 @@ static inline int __sync_blockdev(struct block_device *bdev, int wait)
 /*
  * buffer.c
  */
-extern void guard_bio_eod(int rw, struct bio *bio);
+extern void guard_bio_eod(struct bio *bio);
 extern int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
 		get_block_t *get_block, struct iomap *iomap);
 

fs/mpage.c

@@ -62,7 +62,7 @@ static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
 {
 	bio->bi_end_io = mpage_end_io;
 	bio_set_op_attrs(bio, op, op_flags);
-	guard_bio_eod(op, bio);
+	guard_bio_eod(bio);
 	submit_bio(bio);
 	return NULL;
 }