linux-kernel - Re: [PATCH] bpf: Call cond_resched() to avoid soft lockup in trie

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Message-ID: <CAENh_SQPLHC8pswTRoqh0bQR84HHQmnO3bM07UQa1Xu9uY_3WA@mail.gmail.com>
Date: Tue, 17 Jun 2025 10:42:57 +0100
From: Matt Fleming <matt@...dmodwrite.com>
To: Song Liu <song@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...udflare.com, 
	Matt Fleming <mfleming@...udflare.com>
Subject: Re: [PATCH] bpf: Call cond_resched() to avoid soft lockup in trie_free()

On Mon, Jun 16, 2025 at 4:51 PM Song Liu <song@...nel.org> wrote:
>
> On Mon, Jun 16, 2025 at 2:55 AM Matt Fleming <matt@...dmodwrite.com> wrote:
> >
> > From: Matt Fleming <mfleming@...udflare.com>
> >
> > Calls to kfree() in trie_free() can be expensive for KASAN-enabled
> > kernels. This can cause soft lockup warnings when traversing large maps,
>
> I think this could also happen to KASAN-disabled kernels, so the commit log
> is a bit misleading.

This issue can definitely affect KASAN-disabled kernels.

I mentioned KASAN to give context and explain why I saw this and
nobody else seems to have reported it. I'm happy to reword this part
of the commit message if needed but I still think it should mention
KASAN somewhere because that's the reason I discovered it.

Thanks,
Matt