[PATCH bpf-next 01/19] bpf: Remove migrate_{disable|enable} from LPM trie

[Hou Tao <houtao@xxxxxxxxxxxxxxx>]

From: Hou Tao <houtao1@xxxxxxxxxx>

Both bpf program and bpf syscall may invoke ->update or ->delete
operation for LPM trie. For bpf program, its running context has already
disabled migration explicitly through (migrate_disable()) or implicitly
through (preempt_disable() or disable irq). For bpf syscall, the
migration is disabled through the use of bpf_disable_instrumentation()
before invoking the corresponding map operation callback.

Therefore, it is safe to remove the migrate_{disable|enable){} pair from
LPM trie. To ensure the guarantee will not be voilated later, also add
cant_migrate() check in both update and delete operation.

Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 kernel/bpf/lpm_trie.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index f8bc1e096182..1a3585a485df 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -289,16 +289,11 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 }
 
 static struct lpm_trie_node *lpm_trie_node_alloc(struct lpm_trie *trie,
-						 const void *value,
-						 bool disable_migration)
+						 const void *value)
 {
 	struct lpm_trie_node *node;
 
-	if (disable_migration)
-		migrate_disable();
 	node = bpf_mem_cache_alloc(&trie->ma);
-	if (disable_migration)
-		migrate_enable();
 
 	if (!node)
 		return NULL;
@@ -342,10 +337,10 @@ static long trie_update_elem(struct bpf_map *map,
 	if (key->prefixlen > trie->max_prefixlen)
 		return -EINVAL;
 
-	/* Allocate and fill a new node. Need to disable migration before
-	 * invoking bpf_mem_cache_alloc().
-	 */
-	new_node = lpm_trie_node_alloc(trie, value, true);
+	cant_migrate();
+
+	/* Allocate and fill a new node */
+	new_node = lpm_trie_node_alloc(trie, value);
 	if (!new_node)
 		return -ENOMEM;
 
@@ -425,8 +420,7 @@ static long trie_update_elem(struct bpf_map *map,
 		goto out;
 	}
 
-	/* migration is disabled within the locked scope */
-	im_node = lpm_trie_node_alloc(trie, NULL, false);
+	im_node = lpm_trie_node_alloc(trie, NULL);
 	if (!im_node) {
 		trie->n_entries--;
 		ret = -ENOMEM;
@@ -452,11 +446,9 @@ static long trie_update_elem(struct bpf_map *map,
 out:
 	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
 
-	migrate_disable();
 	if (ret)
 		bpf_mem_cache_free(&trie->ma, new_node);
 	bpf_mem_cache_free_rcu(&trie->ma, free_node);
-	migrate_enable();
 
 	return ret;
 }
@@ -477,6 +469,8 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	if (key->prefixlen > trie->max_prefixlen)
 		return -EINVAL;
 
+	cant_migrate();
+
 	raw_spin_lock_irqsave(&trie->lock, irq_flags);
 
 	/* Walk the tree looking for an exact key/length match and keeping
@@ -555,10 +549,8 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 out:
 	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
 
-	migrate_disable();
 	bpf_mem_cache_free_rcu(&trie->ma, free_parent);
 	bpf_mem_cache_free_rcu(&trie->ma, free_node);
-	migrate_enable();
 
 	return ret;
 }
-- 
2.29.2