netdev - [PATCH bpf-next] bpf: Call maybe_wait_bpf_programs() only once from generic_map_delete

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Message-Id: <20220218181801.2971275-1-eric.dumazet@gmail.com>
Date:   Fri, 18 Feb 2022 10:18:01 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        bpf <bpf@...r.kernel.org>, Stanislav Fomichev <sdf@...gle.com>,
        Brian Vazquez <brianvv@...gle.com>
Subject: [PATCH bpf-next] bpf: Call maybe_wait_bpf_programs() only once from generic_map_delete_batch()

From: Eric Dumazet <edumazet@...gle.com>

As stated in the comment found in maybe_wait_bpf_programs(),
the synchronize_rcu() barrier is only needed before returning
to userspace, not after each deletion in the batch.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Stanislav Fomichev <sdf@...gle.com>
Cc: Brian Vazquez <brianvv@...gle.com>
---
 kernel/bpf/syscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a72f63d5a7daee057bcec3fa6119aca32e2945f7..9c7a72b65eee0ec8d54d36e2c0ab9ff4962091af 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1352,7 +1352,6 @@ int generic_map_delete_batch(struct bpf_map *map,
 		err = map->ops->map_delete_elem(map, key);
 		rcu_read_unlock();
 		bpf_enable_instrumentation();
-		maybe_wait_bpf_programs(map);
 		if (err)
 			break;
 		cond_resched();
@@ -1361,6 +1360,8 @@ int generic_map_delete_batch(struct bpf_map *map,
 		err = -EFAULT;
 
 	kvfree(key);
+
+	maybe_wait_bpf_programs(map);
 	return err;
 }
 
-- 
2.35.1.473.g83b2b277ed-goog