[-stable,6.1 13/17] netfilter: nft_set_rbtree: use read spinlock to avoid datapath contention

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commit 96b33300fba880ec0eafcf3d82486f3463b4b6da upstream.

rbtree GC does not modify the datastructure, instead it collects expired
elements and it enqueues a GC transaction. Use a read spinlock instead
to avoid data contention while GC worker is running.

Fixes: f6c383b8c31a ("netfilter: nf_tables: adapt set backend to use GC transaction API")
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
 net/netfilter/nft_set_rbtree.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index f250b5399344..70491ba98dec 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -622,8 +622,7 @@ static void nft_rbtree_gc(struct work_struct *work)
 	if (!gc)
 		goto done;
-	write_lock_bh(&priv->lock);
-	write_seqcount_begin(&priv->count);
+	read_lock_bh(&priv->lock);
 	for (node = rb_first(&priv->root); node != NULL; node = rb_next(node)) {
 		/* Ruleset has been updated, try later. */
@@ -673,8 +672,7 @@ static void nft_rbtree_gc(struct work_struct *work)
 	gc = nft_trans_gc_catchall(gc, gc_seq);
-	write_seqcount_end(&priv->count);
-	write_unlock_bh(&priv->lock);
+	read_unlock_bh(&priv->lock);
 	if (gc)

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