linux-kernel - [PATCH 2/3] ocfs2: Remove a useless spinlock

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Date:   Tue, 19 Jul 2022 12:01:35 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        ocfs2-devel@....oracle.com
Subject: [PATCH 2/3] ocfs2: Remove a useless spinlock

'node_map_lock' is a spinlock only used to protect calls to set_bit(),
clear_bit() and test_bit().

{set|clear}_bit() are already atomic and don't need this extra spinlock.
test_bit() only reads the bitmap for a given bit.

Remove this useless spinlock.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
test_bit() is NOT documented as an atomic function. However, I can't see
how it could return a wrong result here.

So review with care. There is maybe something I don't think about that is
lurking here.
---
 fs/ocfs2/heartbeat.c | 11 ++++-------
 fs/ocfs2/ocfs2.h     |  2 --
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/fs/ocfs2/heartbeat.c b/fs/ocfs2/heartbeat.c
index 1d72e0788943..4863ad35c242 100644
--- a/fs/ocfs2/heartbeat.c
+++ b/fs/ocfs2/heartbeat.c
@@ -35,7 +35,6 @@ static void ocfs2_node_map_init(struct ocfs2_node_map *map)
 
 void ocfs2_init_node_maps(struct ocfs2_super *osb)
 {
-	spin_lock_init(&osb->node_map_lock);
 	ocfs2_node_map_init(&osb->osb_recovering_orphan_dirs);
 }
 
@@ -67,9 +66,8 @@ void ocfs2_node_map_set_bit(struct ocfs2_super *osb,
 	if (bit==-1)
 		return;
 	BUG_ON(bit >= map->num_nodes);
-	spin_lock(&osb->node_map_lock);
+
 	set_bit(bit, map->map);
-	spin_unlock(&osb->node_map_lock);
 }
 
 void ocfs2_node_map_clear_bit(struct ocfs2_super *osb,
@@ -79,9 +77,8 @@ void ocfs2_node_map_clear_bit(struct ocfs2_super *osb,
 	if (bit==-1)
 		return;
 	BUG_ON(bit >= map->num_nodes);
-	spin_lock(&osb->node_map_lock);
+
 	clear_bit(bit, map->map);
-	spin_unlock(&osb->node_map_lock);
 }
 
 int ocfs2_node_map_test_bit(struct ocfs2_super *osb,
@@ -89,13 +86,13 @@ int ocfs2_node_map_test_bit(struct ocfs2_super *osb,
 			    int bit)
 {
 	int ret;
+
 	if (bit >= map->num_nodes) {
 		mlog(ML_ERROR, "bit=%d map->num_nodes=%d\n", bit, map->num_nodes);
 		BUG();
 	}
-	spin_lock(&osb->node_map_lock);
+
 	ret = test_bit(bit, map->map);
-	spin_unlock(&osb->node_map_lock);
 	return ret;
 }
 
diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index 740b64238312..1df193b97c30 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -302,8 +302,6 @@ struct ocfs2_super
 
 	u32 *slot_recovery_generations;
 
-	spinlock_t node_map_lock;
-
 	u64 root_blkno;
 	u64 system_dir_blkno;
 	u64 bitmap_blkno;
-- 
2.34.1