linux-kernel - Re: [PATCH v2] kernel: bpf: stackmap: fix a possible sleep-in-atomic bug in bpf_mmap_unlock_get_irq

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Date:   Mon, 20 Mar 2023 08:20:36 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Teng Qi <starmiku1207184332@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        baijiaju1990@...look.com
Subject: Re: [PATCH v2] kernel: bpf: stackmap: fix a possible sleep-in-atomic
 bug in bpf_mmap_unlock_get_irq_work()

On Mon, Mar 20, 2023 at 5:28 AM Teng Qi <starmiku1207184332@...il.com> wrote:
>
> Yeah, we got your points. There are two key questions. The first question is
> that preempt_disable() and preempt_enable() will be conflicted with vfree()
> before the mmap_read_unlock().

What does this sentence mean?

> The second question is that thousands callers
> of up_read() only make sure irqs_disabled() == false needed fixed if
> the mmap_read_unlock() is fixed.

that doesn't answer my question either.

> Detecting ebpf bugs can be challenging since it is difficult to prove that a
> bug can be triggered during runtime, as well as fixing the bug. We decided to
> give up this patch that fixes the possible sleep-in-atomic bug in
> bpf_mmap_unlock_get_irq_work(). Instead, we will focus on improving our static
> analysis tool to find ebpf-specific bugs.

Please don't.