linux-kernel - Re: [PATCH] bpf/perf: Fix suspicious RCU usage in get_callchain

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Message-Id: <20260204091419.887114-1-wangqing7171@gmail.com>
Date: Wed,  4 Feb 2026 17:14:19 +0800
From: Qing Wang <wangqing7171@...il.com>
To: andrii.nakryiko@...il.com
Cc: acme@...nel.org,
	andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
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	kpsingh@...nel.org,
	linux-kernel@...r.kernel.org,
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	martin.lau@...ux.dev,
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	song@...nel.org,
	syzbot+72a43cdb78469f7fbad1@...kaller.appspotmail.com,
	wangqing7171@...il.com,
	yonghong.song@...ux.dev
Subject: Re: [PATCH] bpf/perf: Fix suspicious RCU usage in get_callchain_entry()

On Wed, 04 Feb 2026 at 08:04, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> rcu_read_lock/unlock is not called when may_fault == false because in
> that case BPF program is already running within rcu_read_lock/unlock
> region. So I'm not sure this patch fixes anything really. And even
> with trace_in, if we cann rcu_read_lock/unlock one extra time it
> shouldn't be a problem, no?

Thanks for your review, I agree with you. My patch is incorrect and there was a patch series [0]
to fix it.

    [0] https://lore.kernel.org/bpf/fb745675-e25c-4dcc-be4b-4a4411056755@linux.dev/T/#mc0fc5e0fec2e6456f72f402308fd4e397ba19d09

Let's forget my patch.

Thanks,
Qing.