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From: John Ogness <john.ogness@linutronix.de>
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To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, Alexei Starovoitov
 <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko
 <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, Eduard
 Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, Yonghong Song
 <yonghong.song@linux.dev>, John Fastabend <john.fastabend@gmail.com>, KP
 Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@fomichev.me>, Hao Luo
 <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, Petr Mladek
 <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>, Sergey
 Senozhatsky <senozhatsky@chromium.org>
Cc: bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: defer printk() inside __bpf_prog_run()
In-Reply-To: <345098dc-8cb4-4808-98cf-fa9ab3af4fc4@I-love.SAKURA.ne.jp>
References: <345098dc-8cb4-4808-98cf-fa9ab3af4fc4@I-love.SAKURA.ne.jp>
Date: Tue, 25 Jun 2024 16:23:51 +0206
Message-ID: <87ed8lxg1c.fsf@jogness.linutronix.de>
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On 2024-06-25, Tetsuo Handa <penguin-kernel@I-love.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