linux-kernel - [PATCH v2 2/2] libnvdimm/badrange: eliminate a meaningless spinlock operation

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Date:   Sat, 19 Sep 2020 18:45:46 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Oliver O'Halloran <oohall@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Dave Jiang" <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Markus Elfring <Markus.Elfring@....de>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>,
        Libin <huawei.libin@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: [PATCH v2 2/2] libnvdimm/badrange: eliminate a meaningless spinlock operation

badrange_add() take the lock "badrange->lock", but it's released
immediately in add_badrange(), protect nothing.

The pseudo code is as follows:
In badrange_add():
	spin_lock(&badrange->lock);	<---------------
	rc = add_badrange(badrange, addr, length);	|
In add_badrange():					|
	//do nothing					|
	spin_unlock(&badrange->lock);	<---------------
	bre_new = kzalloc(sizeof(*bre_new), GFP_KERNEL);
	spin_lock(&badrange->lock);	<--- lock again

This lock/unlock operation is meaningless.

Because the static function add_badrange() is only called by
badrange_add(), so move its content into badrange_add() then delete it.
By the way, move "kfree(bre_new)" out of the lock protection, it really
doesn't need.

Fixes: b3b454f694db ("libnvdimm: fix clear poison locking with spinlock ...")
Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 drivers/nvdimm/badrange.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/drivers/nvdimm/badrange.c b/drivers/nvdimm/badrange.c
index 9fdba8c43e8605e..7f78b659057902d 100644
--- a/drivers/nvdimm/badrange.c
+++ b/drivers/nvdimm/badrange.c
@@ -45,12 +45,12 @@ static int alloc_and_append_badrange_entry(struct badrange *badrange,
 	return 0;
 }
 
-static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
+int badrange_add(struct badrange *badrange, u64 addr, u64 length)
 {
 	struct badrange_entry *bre, *bre_new;
 
-	spin_unlock(&badrange->lock);
 	bre_new = kzalloc(sizeof(*bre_new), GFP_KERNEL);
+
 	spin_lock(&badrange->lock);
 
 	/*
@@ -63,6 +63,7 @@ static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
 			/* If length has changed, update this list entry */
 			if (bre->length != length)
 				bre->length = length;
+			spin_unlock(&badrange->lock);
 			kfree(bre_new);
 			return 0;
 		}
@@ -72,22 +73,15 @@ static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
 	 * as any overlapping ranges will get resolved when the list is consumed
 	 * and converted to badblocks
 	 */
-	if (!bre_new)
+	if (!bre_new) {
+		spin_unlock(&badrange->lock);
 		return -ENOMEM;
-	append_badrange_entry(badrange, bre_new, addr, length);
-
-	return 0;
-}
-
-int badrange_add(struct badrange *badrange, u64 addr, u64 length)
-{
-	int rc;
+	}
 
-	spin_lock(&badrange->lock);
-	rc = add_badrange(badrange, addr, length);
+	append_badrange_entry(badrange, bre_new, addr, length);
 	spin_unlock(&badrange->lock);
 
-	return rc;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(badrange_add);
 
-- 
1.8.3