netdev - [PATCH bpf-next 12/19] bpf: Disable migration for bpf_selem_unlink in bpf_local_storage_map

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Message-Id: <20250106081900.1665573-13-houtao@huaweicloud.com>
Date: Mon,  6 Jan 2025 16:18:53 +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 12/19] bpf: Disable migration for bpf_selem_unlink in bpf_local_storage_map_free()

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

bpf_local_storage_map_free() invokes bpf_selem_unlink() to unlink and
free the element from the storage map. It may invoke
bpf_obj_free_fields() to free the special fields in the map value. Since
these special fields may be allocated from bpf memory allocator,
migrate_{disable|enable} pairs are necessary for the freeing of these
objects.

To simplify reasoning about when migrate_disable() is needed for the
freeing of these dynamically-allocated objects, let the caller to
guarantee migration is disabled before invoking bpf_obj_free_fields().

Therefore, the patch moves migrate_{disable|enable} out of the
busy_counter condition and calls migrate_disable() before invoking
bpf_obj_free_fields(). The migrate_{disable|enable} pairs in the
underlying implementation of bpf_obj_free_fields() will be removed by
the following patch.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 kernel/bpf/bpf_local_storage.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 615a3034baeb..b649cf736438 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -905,15 +905,13 @@ void bpf_local_storage_map_free(struct bpf_map *map,
 		while ((selem = hlist_entry_safe(
 				rcu_dereference_raw(hlist_first_rcu(&b->list)),
 				struct bpf_local_storage_elem, map_node))) {
-			if (busy_counter) {
-				migrate_disable();
+			migrate_disable();
+			if (busy_counter)
 				this_cpu_inc(*busy_counter);
-			}
 			bpf_selem_unlink(selem, true);
-			if (busy_counter) {
+			if (busy_counter)
 				this_cpu_dec(*busy_counter);
-				migrate_enable();
-			}
+			migrate_enable();
 			cond_resched_rcu();
 		}
 		rcu_read_unlock();
-- 
2.29.2