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

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Date: Wed, 26 Jun 2024 20:29:26 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, John Ogness
 <john.ogness@...utronix.de>, 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>, Sergey Senozhatsky <senozhatsky@...omium.org>, bpf
 <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: defer printk() inside __bpf_prog_run()

On Thu, 27 Jun 2024 09:21:38 +0900
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:

> What change do you propose?
> 
> https://syzkaller.appspot.com/text?tag=Patch&x=121c92fe180000 ?

That's one solution, but you need to call printk_deferred_enter()
*after* taking the lock, otherwise preemption could still be enabled
and you could schedule and migrate between the printk_deferred_enter()
and taking of the lock.

-- Steve