From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Jiri Olsa <jolsa@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18.y 2/5] bpf: Factor stackid_fastpath function from __bpf_get_stackid
Date: Tue, 8 Sep 2026 09:12:06 -0400 [thread overview]
Message-ID: <20260908131209.2236373-2-sashal@kernel.org> (raw)
In-Reply-To: <20260908131209.2236373-1-sashal@kernel.org>
From: Jiri Olsa <jolsa@kernel.org>
[ Upstream commit 0ca56befcffec3a6c9d1842eae06c74e1cf41f11 ]
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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260803210149.296496-3-jolsa@kernel.org
Stable-dep-of: 15f1bd857466 ("bpf: Disable preemption in bpf_get_stackid")
Signed-off-by: Sasha Levin <sashal@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 db64199dbd6fb..b3661d6f18676 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -253,6 +253,7 @@ struct stackid {
u32 len;
u32 hash;
u32 id;
+ bool hash_matches;
};
static int stackid_init(struct stackid *stackid, struct bpf_map *map,
@@ -273,28 +274,46 @@ 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;
@@ -309,7 +328,7 @@ 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;
@@ -319,12 +338,6 @@ 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))
--
2.53.0
next prev parent reply other threads:[~2026-09-08 13:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 13:51 FAILED: patch "[PATCH] bpf: Disable preemption in bpf_get_stackid" failed to apply to 6.18-stable tree gregkh
2026-09-08 13:12 ` [PATCH 6.18.y 1/5] bpf: Factor stackid_init function from __bpf_get_stackid Sasha Levin
2026-09-08 13:12 ` Sasha Levin [this message]
2026-09-08 13:12 ` [PATCH 6.18.y 3/5] bpf: Factor stackid_new_bucket " Sasha Levin
2026-09-08 13:12 ` [PATCH 6.18.y 4/5] bpf: Use stack id functions instead of __bpf_get_stackid Sasha Levin
2026-09-08 13:12 ` [PATCH 6.18.y 5/5] bpf: Disable preemption in bpf_get_stackid Sasha Levin
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