1 files changed, 25 insertions, 33 deletions

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 1e35a2327478..5873d4f1094f 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -1190,22 +1190,19 @@ static noinline void finish_rmw(struct btrfs_raid_bio *rbio)
 	int nr_data = rbio->nr_data;
 	int stripe;
 	int pagenr;
-	int p_stripe = -1;
-	int q_stripe = -1;
+	bool has_qstripe;
 	struct bio_list bio_list;
 	struct bio *bio;
 	int ret;
 
 	bio_list_init(&bio_list);
 
-	if (rbio->real_stripes - rbio->nr_data == 1) {
-		p_stripe = rbio->real_stripes - 1;
-	} else if (rbio->real_stripes - rbio->nr_data == 2) {
-		p_stripe = rbio->real_stripes - 2;
-		q_stripe = rbio->real_stripes - 1;
-	} else {
+	if (rbio->real_stripes - rbio->nr_data == 1)
+		has_qstripe = false;
+	else if (rbio->real_stripes - rbio->nr_data == 2)
+		has_qstripe = true;
+	else
 		BUG();
-	}
 
 	/* at this point we either have a full stripe,
 	 * or we've read the full stripe from the drive.
@@ -1249,7 +1246,7 @@ static noinline void finish_rmw(struct btrfs_raid_bio *rbio)
 		SetPageUptodate(p);
 		pointers[stripe++] = kmap(p);
 
-		if (q_stripe != -1) {
+		if (has_qstripe) {
 
 			/*
 			 * raid6, add the qstripe and call the
@@ -2325,8 +2322,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 	int nr_data = rbio->nr_data;
 	int stripe;
 	int pagenr;
-	int p_stripe = -1;
-	int q_stripe = -1;
+	bool has_qstripe;
 	struct page *p_page = NULL;
 	struct page *q_page = NULL;
 	struct bio_list bio_list;
@@ -2336,14 +2332,12 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 
 	bio_list_init(&bio_list);
 
-	if (rbio->real_stripes - rbio->nr_data == 1) {
-		p_stripe = rbio->real_stripes - 1;
-	} else if (rbio->real_stripes - rbio->nr_data == 2) {
-		p_stripe = rbio->real_stripes - 2;
-		q_stripe = rbio->real_stripes - 1;
-	} else {
+	if (rbio->real_stripes - rbio->nr_data == 1)
+		has_qstripe = false;
+	else if (rbio->real_stripes - rbio->nr_data == 2)
+		has_qstripe = true;
+	else
 		BUG();
-	}
 
 	if (bbio->num_tgtdevs && bbio->tgtdev_map[rbio->scrubp]) {
 		is_replace = 1;
@@ -2365,17 +2359,22 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 		goto cleanup;
 	SetPageUptodate(p_page);
 
-	if (q_stripe != -1) {
+	if (has_qstripe) {
+		/* RAID6, allocate and map temp space for the Q stripe */
 		q_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 		if (!q_page) {
 			__free_page(p_page);
 			goto cleanup;
 		}
 		SetPageUptodate(q_page);
+		pointers[rbio->real_stripes - 1] = kmap(q_page);
 	}
 
 	atomic_set(&rbio->error, 0);
 
+	/* Map the parity stripe just once */
+	pointers[nr_data] = kmap(p_page);
+
 	for_each_set_bit(pagenr, rbio->dbitmap, rbio->stripe_npages) {
 		struct page *p;
 		void *parity;
@@ -2385,17 +2384,8 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 			pointers[stripe] = kmap(p);
 		}
 
-		/* then add the parity stripe */
-		pointers[stripe++] = kmap(p_page);
-
-		if (q_stripe != -1) {
-
-			/*
-			 * raid6, add the qstripe and call the
-			 * library function to fill in our p/q
-			 */
-			pointers[stripe++] = kmap(q_page);
-
+		if (has_qstripe) {
+			/* RAID6, call the library function to fill in our P/Q */
 			raid6_call.gen_syndrome(rbio->real_stripes, PAGE_SIZE,
 						pointers);
 		} else {
@@ -2416,12 +2406,14 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 
 		for (stripe = 0; stripe < nr_data; stripe++)
 			kunmap(page_in_rbio(rbio, stripe, pagenr, 0));
-		kunmap(p_page);
 	}
 
+	kunmap(p_page);
 	__free_page(p_page);
-	if (q_page)
+	if (q_page) {
+		kunmap(q_page);
 		__free_page(q_page);
+	}
 
 writeback:
 	/*