netdev - [PATCH bpf-next 19/19] bpf: Remove migrate_{disable|enable} from bpf_selem

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Message-Id: <20250106081900.1665573-20-houtao@huaweicloud.com>
Date: Mon,  6 Jan 2025 16:19:00 +0800
From: Hou Tao <houtao@...weicloud.com>
To: bpf@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Hao Luo <haoluo@...gle.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	Daniel Borkmann <daniel@...earbox.net>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Jiri Olsa <jolsa@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	houtao1@...wei.com,
	xukuohai@...wei.com
Subject: [PATCH bpf-next 19/19] bpf: Remove migrate_{disable|enable} from bpf_selem_free()

From: Hou Tao <houtao1@...wei.com>

bpf_selem_free() has the following three callers:

(1) bpf_local_storage_update
It will be invoked through ->map_update_elem syscall or helpers for
storage map. Migration has already been disabled in these running
contexts.

(2) bpf_sk_storage_clone
It has already disabled migration before invoking bpf_selem_free().

(3) bpf_selem_free_list
bpf_selem_free_list() has three callers: bpf_selem_unlink_storage(),
bpf_local_storage_update() and bpf_local_storage_destroy().

The callers of bpf_selem_unlink_storage() includes: storage map
->map_delete_elem syscall, storage map delete helpers and
bpf_local_storage_map_free(). These contexts have already disabled
migration when invoking bpf_selem_unlink() which invokes
bpf_selem_unlink_storage() and bpf_selem_free_list() correspondingly.

bpf_local_storage_update() has been analyzed as the first caller above.
bpf_local_storage_destroy() is invoked when freeing the local storage
for the kernel object. Now cgroup, task, inode and sock storage have
already disabled migration before invoking bpf_local_storage_destroy().

After the analyses above, it is safe to remove migrate_{disable|enable}
from bpf_selem_free(). Also add a cant_migrate() check in
bpf_selem_free().

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 kernel/bpf/bpf_local_storage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index d67ba116aee8..f196093db0a0 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -235,6 +235,8 @@ void bpf_selem_free(struct bpf_local_storage_elem *selem,
 		    struct bpf_local_storage_map *smap,
 		    bool reuse_now)
 {
+	cant_migrate();
+
 	if (!smap->bpf_ma) {
 		/* Only task storage has uptrs and task storage
 		 * has moved to bpf_mem_alloc. Meaning smap->bpf_ma == true
@@ -258,9 +260,7 @@ void bpf_selem_free(struct bpf_local_storage_elem *selem,
 		 * bpf_mem_cache_free will be able to reuse selem
 		 * immediately.
 		 */
-		migrate_disable();
 		bpf_mem_cache_free(&smap->selem_ma, selem);
-		migrate_enable();
 		return;
 	}
 
-- 
2.29.2