linux-kernel - Re: [PATCH] bpf: defer printk() inside __bpf_prog

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Message-ID: <87ed8lxg1c.fsf@jogness.linutronix.de>
Date: Tue, 25 Jun 2024 16:23:51 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, 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>, Song Liu <song@...nel.org>, 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>, Petr Mladek
 <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, Sergey
 Senozhatsky <senozhatsky@...omium.org>
Cc: bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: defer printk() inside __bpf_prog_run()

On 2024-06-25, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:
> syzbot is reporting circular locking dependency inside __bpf_prog_run(),
> for fault injection calls printk() despite rq lock is already held.
>
> Guard __bpf_prog_run() using printk_deferred_{enter,exit}() (and
> preempt_{disable,enable}() if CONFIG_PREEMPT_RT=n) in order to defer any
> printk() messages.

Why is the reason for disabling preemption?

John Ogness