bpf: Remove migrate_{disable|enable} from bpf_selem_free()

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().

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20250108010728.207536-17-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Hou Tao

kernel/bpf/bpf_local_storage.c

@@ -254,9 +254,7 @@ 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;
 	}