btrfs: scrub: use pointer array to replace sblocks_for_recheck

In function scrub_handle_errored_block(), we use @sblocks_for_recheck
pointer to hold one scrub_block for each mirror, and uses kcalloc() to
allocate an array.

But this one pointer for an array is not readable due to the member
offsets done by addition and not [].

Change this pointer to struct scrub_block *[BTRFS_MAX_MIRRORS], this
will slightly increase the stack memory usage.

Since function scrub_handle_errored_block() won't get iterative calls,
this extra cost would completely be acceptable.

And since we're here, also set sblock->refs and use scrub_block_put() to
clean them up, as later we will add extra members in scrub_block, which
needs scrub_block_put() to clean them up.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -203,7 +203,7 @@ struct full_stripe_lock {
 };
 
 static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
-				     struct scrub_block *sblocks_for_recheck);
+				     struct scrub_block *sblocks_for_recheck[]);
 static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
 				struct scrub_block *sblock,
 				int retry_failed_mirror);
@@ -817,7 +817,8 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 	unsigned int failed_mirror_index;
 	unsigned int is_metadata;
 	unsigned int have_csum;
-	struct scrub_block *sblocks_for_recheck; /* holds one for each mirror */
+	/* One scrub_block for each mirror */
+	struct scrub_block *sblocks_for_recheck[BTRFS_MAX_MIRRORS] = { 0 };
 	struct scrub_block *sblock_bad;
 	int ret;
 	int mirror_index;
@@ -910,10 +911,10 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 	 * repaired area is verified in order to correctly maintain
 	 * the statistics.
 	 */
-
-	sblocks_for_recheck = kcalloc(BTRFS_MAX_MIRRORS,
-				      sizeof(*sblocks_for_recheck), GFP_KERNEL);
-	if (!sblocks_for_recheck) {
+	for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
+		sblocks_for_recheck[mirror_index] =
+			kzalloc(sizeof(struct scrub_block), GFP_KERNEL);
+		if (!sblocks_for_recheck[mirror_index]) {
 			spin_lock(&sctx->stat_lock);
 			sctx->stat.malloc_errors++;
 			sctx->stat.read_errors++;
@@ -922,6 +923,15 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 			btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
 			goto out;
 		}
+		/*
+		 * Note: the two members refs and outstanding_sectors are not
+		 * used in the blocks that are used for the recheck procedure.
+		 * But to make the cleanup easier, we just put one ref for each
+		 * sblocks.
+		 */
+		refcount_set(&sblocks_for_recheck[mirror_index]->refs, 1);
+		sblocks_for_recheck[mirror_index]->sctx = sctx;
+	}
 
 	/* Setup the context, map the logical blocks and alloc the sectors */
 	ret = scrub_setup_recheck_block(sblock_to_check, sblocks_for_recheck);
@@ -934,7 +944,7 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 		goto out;
 	}
 	BUG_ON(failed_mirror_index >= BTRFS_MAX_MIRRORS);
-	sblock_bad = sblocks_for_recheck + failed_mirror_index;
+	sblock_bad = sblocks_for_recheck[failed_mirror_index];
 
 	/* build and submit the bios for the failed mirror, check checksums */
 	scrub_recheck_block(fs_info, sblock_bad, 1);
@@ -1019,21 +1029,21 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 		if (!scrub_is_page_on_raid56(sblock_bad->sectors[0])) {
 			if (mirror_index >= BTRFS_MAX_MIRRORS)
 				break;
-			if (!sblocks_for_recheck[mirror_index].sector_count)
+			if (!sblocks_for_recheck[mirror_index]->sector_count)
 				break;
 
-			sblock_other = sblocks_for_recheck + mirror_index;
+			sblock_other = sblocks_for_recheck[mirror_index];
 		} else {
 			struct scrub_recover *r = sblock_bad->sectors[0]->recover;
 			int max_allowed = r->bioc->num_stripes - r->bioc->num_tgtdevs;
 
 			if (mirror_index >= max_allowed)
 				break;
-			if (!sblocks_for_recheck[1].sector_count)
+			if (!sblocks_for_recheck[1]->sector_count)
 				break;
 
 			ASSERT(failed_mirror_index == 0);
-			sblock_other = sblocks_for_recheck + 1;
+			sblock_other = sblocks_for_recheck[1];
 			sblock_other->sectors[0]->mirror_num = 1 + mirror_index;
 		}
 
@@ -1105,12 +1115,11 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 			/* Try to find no-io-error sector in mirrors */
 			for (mirror_index = 0;
 			     mirror_index < BTRFS_MAX_MIRRORS &&
-			     sblocks_for_recheck[mirror_index].sector_count > 0;
+			     sblocks_for_recheck[mirror_index]->sector_count > 0;
 			     mirror_index++) {
-				if (!sblocks_for_recheck[mirror_index].
+				if (!sblocks_for_recheck[mirror_index]->
 				    sectors[sector_num]->io_error) {
-					sblock_other = sblocks_for_recheck +
-						       mirror_index;
+					sblock_other = sblocks_for_recheck[mirror_index];
 					break;
 				}
 			}
@@ -1184,25 +1193,28 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 	}
 
 out:
-	if (sblocks_for_recheck) {
-		for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS;
-		     mirror_index++) {
-			struct scrub_block *sblock = sblocks_for_recheck +
-						     mirror_index;
+	for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
+		struct scrub_block *sblock = sblocks_for_recheck[mirror_index];
 		struct scrub_recover *recover;
-			int i;
+		int sector_index;
 
-			for (i = 0; i < sblock->sector_count; i++) {
-				sblock->sectors[i]->sblock = NULL;
-				recover = sblock->sectors[i]->recover;
+		/* Not allocated, continue checking the next mirror */
+		if (!sblock)
+			continue;
+
+		for (sector_index = 0; sector_index < sblock->sector_count;
+		     sector_index++) {
+			/*
+			 * Here we just cleanup the recover, each sector will be
+			 * properly cleaned up by later scrub_block_put()
+			 */
+			recover = sblock->sectors[sector_index]->recover;
 			if (recover) {
 				scrub_put_recover(fs_info, recover);
-					sblock->sectors[i]->recover = NULL;
-				}
-				scrub_sector_put(sblock->sectors[i]);
+				sblock->sectors[sector_index]->recover = NULL;
 			}
 		}
-		kfree(sblocks_for_recheck);
+		scrub_block_put(sblock);
 	}
 
 	ret = unlock_full_stripe(fs_info, logical, full_stripe_locked);
@@ -1252,7 +1264,7 @@ static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
 }
 
 static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
-				     struct scrub_block *sblocks_for_recheck)
+				     struct scrub_block *sblocks_for_recheck[])
 {
 	struct scrub_ctx *sctx = original_sblock->sctx;
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
@@ -1272,11 +1284,6 @@ static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
 	int nmirrors;
 	int ret;
 
-	/*
-	 * Note: the two members refs and outstanding_sectors are not used (and
-	 * not set) in the blocks that are used for the recheck procedure.
-	 */
-
 	while (length > 0) {
 		sublen = min_t(u64, length, fs_info->sectorsize);
 		mapped_length = sublen;
@@ -1315,7 +1322,7 @@ static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
 			struct scrub_block *sblock;
 			struct scrub_sector *sector;
 
-			sblock = sblocks_for_recheck + mirror_index;
+			sblock = sblocks_for_recheck[mirror_index];
 			sblock->sctx = sctx;
 
 			sector = kzalloc(sizeof(*sector), GFP_NOFS);