From 542582fce1700c01b12e7945aaf173074e008e3e Mon Sep 17 00:00:00 2001
From: Alex Elder <elder@inktank.com>
Date: Thu, 9 Aug 2012 10:33:25 -0700
Subject: rbd: bio_chain_clone() cleanups

In bio_chain_clone(), at the end of the function the bi_next field
of the tail of the new bio chain is nulled.  This isn't necessary,
because if "tail" is non-null, its value will be the last bio
structure allocated at the top of the while loop in that function.
And before that structure is added to the end of the new chain, its
bi_next pointer is always made null.

While touching that function, clean a few other things:
    - define each local variable on its own line
    - move the definition of "tmp" to an inner scope
    - move the modification of gfpmask closer to where it's used
    - rearrange the logic that sets the chain's tail pointer

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index cf44da8..43f6ef8 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -754,7 +754,9 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
 				   struct bio_pair **bp,
 				   int len, gfp_t gfpmask)
 {
-	struct bio *tmp, *old_chain = *old, *new_chain = NULL, *tail = NULL;
+	struct bio *old_chain = *old;
+	struct bio *new_chain = NULL;
+	struct bio *tail;
 	int total = 0;
 
 	if (*bp) {
@@ -763,9 +765,12 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
 	}
 
 	while (old_chain && (total < len)) {
+		struct bio *tmp;
+
 		tmp = bio_kmalloc(gfpmask, old_chain->bi_max_vecs);
 		if (!tmp)
 			goto err_out;
+		gfpmask &= ~__GFP_WAIT;	/* can't wait after the first */
 
 		if (total + old_chain->bi_size > len) {
 			struct bio_pair *bp;
@@ -793,15 +798,12 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
 		}
 
 		tmp->bi_bdev = NULL;
-		gfpmask &= ~__GFP_WAIT;
 		tmp->bi_next = NULL;
-
-		if (!new_chain) {
-			new_chain = tail = tmp;
-		} else {
+		if (new_chain)
 			tail->bi_next = tmp;
-			tail = tmp;
-		}
+		else
+			new_chain = tmp;
+		tail = tmp;
 		old_chain = old_chain->bi_next;
 
 		total += tmp->bi_size;
@@ -809,9 +811,6 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
 
 	BUG_ON(total < len);
 
-	if (tail)
-		tail->bi_next = NULL;
-
 	*old = old_chain;
 
 	return new_chain;
-- 
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