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@xxxxxxxxxx>
> ---
> 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
-
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