The new stackid_fastpath does the fast stack hash and trace check, that
does not need new bucket allocation. It covers both just-ip and buildid
code paths.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/bpf/stackmap.c | 43 ++++++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 0eafe55b1828..7bc2a966e3e8 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -511,6 +511,7 @@ struct stackid {
 	u32  len;
 	u32  hash;
 	u32  id;
+	bool hash_matches;
 };
 
 static int stackid_init(struct stackid *stackid, struct bpf_map *map,
@@ -531,28 +532,46 @@ static int stackid_init(struct stackid *stackid, struct bpf_map *map,
 	stackid->hash = jhash2((u32 *)stackid->ips, stackid->len / sizeof(u32), 0);
 	stackid->id = stackid->hash & (smap->n_buckets - 1);
 	stackid->bucket = READ_ONCE(smap->buckets[stackid->id]);
+	stackid->hash_matches = stackid->bucket && stackid->bucket->hash == stackid->hash;
 	return 0;
 }
 
+static int stackid_fastpath(struct stackid *stackid, struct bpf_map *map,
+			    struct perf_callchain_entry *trace, u64 flags)
+{
+	int err;
+
+	err = stackid_init(stackid, map, trace, flags);
+	if (err)
+		return err;
+
+	/* fast cmp */
+	if (stackid->hash_matches && flags & BPF_F_FAST_STACK_CMP)
+		return stackid->id;
+
+	if (stack_map_use_build_id(map))
+		return -ENOENT;
+	if (stackid->hash_matches && stackid->bucket->nr == stackid->nr &&
+	    memcmp(stackid->bucket->data, stackid->ips, stackid->len) == 0)
+		return stackid->id;
+	if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID))
+		return -EEXIST;
+	return -ENOENT;
+}
+
 static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			      struct perf_callchain_entry *trace, u64 flags)
 {
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 	struct stack_map_bucket *new_bucket, *old_bucket;
 	bool user = flags & BPF_F_USER_STACK;
-	bool hash_matches;
 	u32 trace_len, i;
 	int err;
 
-	err = stackid_init(stackid, map, trace, flags);
-	if (err)
+	err = stackid_fastpath(stackid, map, trace, flags);
+	if (err != -ENOENT)
 		return err;
 
-	hash_matches = stackid->bucket && stackid->bucket->hash == stackid->hash;
-	/* fast cmp */
-	if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
-		return stackid->id;
-
 	if (stack_map_use_build_id(map)) {
 		struct bpf_stack_build_id *id_offs;
 
@@ -567,7 +586,7 @@ static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			id_offs[i].ip = stackid->ips[i];
 		stack_map_get_build_id_offset(id_offs, stackid->nr, user, false /* !may_fault */);
 		trace_len = stackid->nr * sizeof(struct bpf_stack_build_id);
-		if (hash_matches && stackid->bucket->nr == stackid->nr &&
+		if (stackid->hash_matches && stackid->bucket->nr == stackid->nr &&
 		    memcmp(stackid->bucket->data, new_bucket->data, trace_len) == 0) {
 			pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 			return stackid->id;
@@ -577,12 +596,6 @@ static long __bpf_get_stackid(struct stackid *stackid, struct bpf_map *map,
 			return -EEXIST;
 		}
 	} else {
-		if (hash_matches && stackid->bucket->nr == stackid->nr &&
-		    memcmp(stackid->bucket->data, stackid->ips, stackid->len) == 0)
-			return stackid->id;
-		if (stackid->bucket && !(flags & BPF_F_REUSE_STACKID))
-			return -EEXIST;
-
 		new_bucket = (struct stack_map_bucket *)
 			pcpu_freelist_pop(&smap->freelist);
 		if (unlikely(!new_bucket))
-- 
2.54.0