Christophe JAILLET
2022-Jul-19 10:01 UTC
[Ocfs2-devel] [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 at wanadoo.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
David Laight
2022-Jul-19 10:24 UTC
[Ocfs2-devel] [PATCH 2/3] ocfs2: Remove a useless spinlock
From: Christophe JAILLET> Sent: 19 July 2022 11:02 > > '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.It looks to me like the calling code is racy unless there is another lock in the callers. While map->map is protected, the result of test_bit() is stale - so can't be used for much. David> > Signed-off-by: Christophe JAILLET <christophe.jaillet at wanadoo.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- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)