linux-kernel - [PATCH 1/1] backing-dev: refactor wb_congested

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Date:   Thu, 12 Mar 2020 00:21:56 +0000
From:   Jules Irenge <jbi.octave@...il.com>
To:     boqun.feng@...il.com
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] backing-dev: refactor wb_congested_put()

wb_congested_put() was written in such a way that made it difficult
	for Sparse tool not to complain
Expanding the function locking block in the if statement improves on
the readability of the code. Rewritting it  comes with one add-on:

It fixes a warning reported by Sparse tool at wb_congested_put()

warning: context imbalance in wb_congested_put() - unexpected unlock

Refactor the function wb_congested_put()

Signed-off-by: Jules Irenge <jbi.octave@...il.com>
---
 mm/backing-dev.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 62f05f605fb5..9d47c0b6a42c 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -464,18 +464,21 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
 {
 	unsigned long flags;
 
-	if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags))
-		return;
-
+	if (!refcount_dec_not_one(&congested->refcnt)) {
+		spin_lock_irqsave(&cgwb_lock, flags);
+		if (!refcount_dec_and_test(&congested->refcnt)) {
+			spin_unlock_irqrestore(&cgwb_lock, flags);
+			return;
+		}
 	/* bdi might already have been destroyed leaving @congested unlinked */
-	if (congested->__bdi) {
-		rb_erase(&congested->rb_node,
-			 &congested->__bdi->cgwb_congested_tree);
-		congested->__bdi = NULL;
+		if (congested->__bdi) {
+			rb_erase(&congested->rb_node,
+				 &congested->__bdi->cgwb_congested_tree);
+			congested->__bdi = NULL;
+		}
+		spin_unlock_irqrestore(&cgwb_lock, flags);
+		kfree(congested);
 	}
-
-	spin_unlock_irqrestore(&cgwb_lock, flags);
-	kfree(congested);
 }
 
 static void cgwb_release_workfn(struct work_struct *work)
-- 
2.24.1