[PATCH bpf-next v2 21/26] bpf: Convert lpm_trie.c to rqspinlock

Kumar Kartikeya Dwivedi
2025-02-06T10:55:07Z

Convert all LPM trie usage of raw_spinlock to rqspinlock.

Note that rcu_dereference_protected in trie_delete_elem is switched over
to plain rcu_dereference, the RCU read lock should be held from BPF
program side or eBPF syscall path, and the trie->lock is just acquired
before the dereference. It is not clear the reason the protected variant
was used from the commit history, but the above reasoning makes sense so
switch over.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
kernel/bpf/lpm_trie.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index e8a772e64324..be66d7e520e0 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -15,6 +15,7 @@
#include <net/ipv6.h>
#include <uapi/linux/btf.h>
#include <linux/btf_ids.h>
+#include <asm/rqspinlock.h>
#include <linux/bpf_mem_alloc.h>

/* Intermediate node */
@@ -36,7 +37,7 @@ struct lpm_trie {
size_t n_entries;
size_t max_prefixlen;
size_t data_size;
- raw_spinlock_t lock;
+ rqspinlock_t lock;
};

/* This trie implements a longest prefix match algorithm that can be used to
@@ -342,7 +343,9 @@ static long trie_update_elem(struct bpf_map *map,
if (!new_node)
return -ENOMEM;

- raw_spin_lock_irqsave(&trie->lock, irq_flags);
+ ret = raw_res_spin_lock_irqsave(&trie->lock, irq_flags);
+ if (ret)
+ goto out_free;

new_node->prefixlen = key->prefixlen;
RCU_INIT_POINTER(new_node->child[0], NULL);
@@ -356,8 +359,7 @@ static long trie_update_elem(struct bpf_map *map,
*/
slot = &trie->root;

- while ((node = rcu_dereference_protected(*slot,
- lockdep_is_held(&trie->lock)))) {
+ while ((node = rcu_dereference(*slot))) {
matchlen = longest_prefix_match(trie, node, key);

if (node->prefixlen != matchlen ||
@@ -442,8 +444,8 @@ static long trie_update_elem(struct bpf_map *map,
rcu_assign_pointer(*slot, im_node);

out:
- raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
-
+ raw_res_spin_unlock_irqrestore(&trie->lock, irq_flags);
+out_free:
if (ret)
bpf_mem_cache_free(&trie->ma, new_node);
bpf_mem_cache_free_rcu(&trie->ma, free_node);
@@ -467,7 +469,9 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
if (key->prefixlen > trie->max_prefixlen)
return -EINVAL;

- raw_spin_lock_irqsave(&trie->lock, irq_flags);
+ ret = raw_res_spin_lock_irqsave(&trie->lock, irq_flags);
+ if (ret)
+ return ret;

/* Walk the tree looking for an exact key/length match and keeping
* track of the path we traverse. We will need to know the node
@@ -478,8 +482,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
trim = &trie->root;
trim2 = trim;
parent = NULL;
- while ((node = rcu_dereference_protected(
- *trim, lockdep_is_held(&trie->lock)))) {
+ while ((node = rcu_dereference(*trim))) {
matchlen = longest_prefix_match(trie, node, key);

if (node->prefixlen != matchlen ||
@@ -543,7 +546,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
free_node = node;

out:
- raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
+ raw_res_spin_unlock_irqrestore(&trie->lock, irq_flags);

bpf_mem_cache_free_rcu(&trie->ma, free_parent);
bpf_mem_cache_free_rcu(&trie->ma, free_node);
@@ -592,7 +595,7 @@ static struct bpf_map *trie_alloc(union bpf_attr *attr)
offsetof(struct bpf_lpm_trie_key_u8, data);
trie->max_prefixlen = trie->data_size * 8;

- raw_spin_lock_init(&trie->lock);
+ raw_res_spin_lock_init(&trie->lock);

/* Allocate intermediate and leaf nodes from the same allocator */
leaf_size = sizeof(struct lpm_trie_node) + trie->data_size +
--
2.43.5