netdev - Re: [PATCH] bpf_lru_list: Read double-checked variable once without lock

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Date:   Thu, 11 Feb 2021 00:00:07 +0000
From:   patchwork-bot+netdevbpf@...nel.org
To:     Marco Elver <elver@...gle.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        paulmck@...nel.org, dvyukov@...gle.com,
        syzbot+3536db46dfa58c573458@...kaller.appspotmail.com,
        syzbot+516acdb03d3e27d91bcd@...kaller.appspotmail.com
Subject: Re: [PATCH] bpf_lru_list: Read double-checked variable once without lock

Hello:

This patch was applied to bpf/bpf-next.git (refs/heads/master):

On Tue,  9 Feb 2021 12:27:01 +0100 you wrote:
> For double-checked locking in bpf_common_lru_push_free(), node->type is
> read outside the critical section and then re-checked under the lock.
> However, concurrent writes to node->type result in data races.
> 
> For example, the following concurrent access was observed by KCSAN:
> 
>   write to 0xffff88801521bc22 of 1 bytes by task 10038 on cpu 1:
>    __bpf_lru_node_move_in        kernel/bpf/bpf_lru_list.c:91
>    __local_list_flush            kernel/bpf/bpf_lru_list.c:298
>    ...
>   read to 0xffff88801521bc22 of 1 bytes by task 10043 on cpu 0:
>    bpf_common_lru_push_free      kernel/bpf/bpf_lru_list.c:507
>    bpf_lru_push_free             kernel/bpf/bpf_lru_list.c:555
>    ...
> 
> [...]

Here is the summary with links:
  - bpf_lru_list: Read double-checked variable once without lock
    https://git.kernel.org/bpf/bpf-next/c/6df8fb83301d

You are awesome, thank you!
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