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

bpf_selem_alloc() has two callers:
(1) bpf_sk_storage_clone_elem()
bpf_sk_storage_clone() has already disabled migration before invoking
bpf_sk_storage_clone_elem().

(2) bpf_local_storage_update()
Its callers include: cgrp/task/inode/sock storage ->map_update_elem()
callbacks and bpf_{cgrp|task|inode|sk}_storage_get() helpers. These
running contexts have already disabled migration

Therefore, there is no need to add extra migrate_{disable|enable} pair
in bpf_selem_alloc().

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20250108010728.207536-14-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Hou Tao

kernel/bpf/bpf_local_storage.c

@@ -81,9 +81,7 @@ bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
 		return NULL;
 
 	if (smap->bpf_ma) {
-		migrate_disable();
 		selem = bpf_mem_cache_alloc_flags(&smap->selem_ma, gfp_flags);
-		migrate_enable();
 		if (selem)
 			/* Keep the original bpf_map_kzalloc behavior
 			 * before started using the bpf_mem_cache_alloc.