md: remove 'idx' from 'struct resync_pages'

bio_add_page() won't fail for resync bio, and the page index for each
bio is same, so remove it.

More importantly the 'idx' of 'struct resync_pages' is initialized in
mempool allocator function, the current way is wrong since mempool is
only responsible for allocation, we can't use that for initialization.

Suggested-by: NeilBrown <[e-mail]>
Reported-by: NeilBrown <[e-mail]>
Reported-and-tested-by: Patrick <[e-mail]>
Fixes: f0250618361d(md: raid10: don't use bio's vec table to manage resync pages)
Fixes: 98d30c5812c3(md: raid1: don't use bio's vec table to manage resync pages)
Cc: [e-mail] (4.12+)
Signed-off-by: Ming Lei <[e-mail]>
Signed-off-by: Shaohua Li <[e-mail]>

drivers/md/md.h

···
 
 /* for managing resync I/O pages */
 struct resync_pages {
-	unsigned	idx;	/* for get/put page from the pool */
 	void		*raid_bio;
 	struct page	*pages[RESYNC_PAGES];
 };

drivers/md/raid1.c

···
 			resync_get_all_pages(rp);
 		}
 
-		rp->idx = 0;
 		rp->raid_bio = r1_bio;
 		bio->bi_private = rp;
 	}
···
 	int good_sectors = RESYNC_SECTORS;
 	int min_bad = 0; /* number of sectors that are bad in all devices */
 	int idx = sector_to_idx(sector_nr);
+	int page_idx = 0;
 
 	if (!conf->r1buf_pool)
 		if (init_resync(conf))
···
 			bio = r1_bio->bios[i];
 			rp = get_resync_pages(bio);
 			if (bio->bi_end_io) {
-				page = resync_fetch_page(rp, rp->idx++);
+				page = resync_fetch_page(rp, page_idx);
 
 				/*
 				 * won't fail because the vec table is big
···
 		nr_sectors += len>>9;
 		sector_nr += len>>9;
 		sync_blocks -= (len>>9);
-	} while (get_resync_pages(r1_bio->bios[disk]->bi_private)->idx < RESYNC_PAGES);
+	} while (++page_idx < RESYNC_PAGES);
 
 	r1_bio->sectors = nr_sectors;
 

drivers/md/raid10.c

···
 			resync_get_all_pages(rp);
 		}
 
-		rp->idx = 0;
 		rp->raid_bio = r10_bio;
 		bio->bi_private = rp;
 		if (rbio) {
···
 	sector_t sectors_skipped = 0;
 	int chunks_skipped = 0;
 	sector_t chunk_mask = conf->geo.chunk_mask;
+	int page_idx = 0;
 
 	if (!conf->r10buf_pool)
 		if (init_resync(conf))
···
 			break;
 		for (bio= biolist ; bio ; bio=bio->bi_next) {
 			struct resync_pages *rp = get_resync_pages(bio);
-			page = resync_fetch_page(rp, rp->idx++);
+			page = resync_fetch_page(rp, page_idx);
 			/*
 			 * won't fail because the vec table is big enough
 			 * to hold all these pages
···
 		}
 		nr_sectors += len>>9;
 		sector_nr += len>>9;
-	} while (get_resync_pages(biolist)->idx < RESYNC_PAGES);
+	} while (++page_idx < RESYNC_PAGES);
 	r10_bio->sectors = nr_sectors;
 
 	while (biolist) {