From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4C8115B7;
	Thu, 27 Jun 2024 00:29:30 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1719448171; cv=none; b=TZCVIVyv5YBi6qXz5/BPlbUjJkESHOX41v8WY7um+cvAttlI0/gGb3CRP7NXlvxoGt0t8+gX+58zzngNDWlXg3WUtxoDQNvoxkR88deGpe18AuWFk8iurFnc50mmmUI1hRdBOv47XExVAJE11o0V5eZwpUqgKRWOGmfIkTNzZ7E=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1719448171; c=relaxed/simple;
	bh=n7RJHgw4rE2gB6R6ed7pCBeKs4Ou/+xitA3UzT+RD+0=;
	h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References:
	 MIME-Version:Content-Type; b=J1OIUgLPsa1hJz083lySve2G35zj5Qy6YpMjvWtY7R2DUcKAsx1Fc6pnbuuc7gBBfi+g9rgMOLLyv/R9vIV4//ZQHlehTIHbAuzmGOdrMjmnHwJLyKWwie4Hp63p8ObDJjiIL1O8AwA1SqMcZy+3h9NwFPwCwaLiB0kcvabLbpo=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201
Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7EBEC116B1;
	Thu, 27 Jun 2024 00:29:27 +0000 (UTC)
Date: Wed, 26 Jun 2024 20:29:26 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>, John Ogness
 <john.ogness@linutronix.de>, 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>, Sergey Senozhatsky <senozhatsky@chromium.org>, bpf
 <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: defer printk() inside __bpf_prog_run()
Message-ID: <20240626202926.4267df74@rorschach.local.home>
In-Reply-To: <290aac9b-0664-404d-a457-292d69f9b22b@I-love.SAKURA.ne.jp>
References: <345098dc-8cb4-4808-98cf-fa9ab3af4fc4@I-love.SAKURA.ne.jp>
	<87ed8lxg1c.fsf@jogness.linutronix.de>
	<60704acc-61bd-4911-bb96-bd1cdd69803d@I-love.SAKURA.ne.jp>
	<87ikxxxbwd.fsf@jogness.linutronix.de>
	<ea56efca-552f-46d7-a7eb-4213c23a263b@I-love.SAKURA.ne.jp>
	<CAADnVQ+hxHsQpfOkQvq4d5AEQsH41BHL+e_RtuxUzyh-vNyYEQ@mail.gmail.com>
	<7edb0e39-a62e-4aac-a292-3cf7ae26ccbd@I-love.SAKURA.ne.jp>
	<CAADnVQKoHk5FTN=jywBjgdTdLwv-c76nCzyH90Js-41WxPK_Tw@mail.gmail.com>
	<744c9c43-9e4f-4069-9773-067036237bff@I-love.SAKURA.ne.jp>
	<20240626122748.065a903b@rorschach.local.home>
	<f6c23073-dc0d-4b3f-b37d-1edb82737b5b@I-love.SAKURA.ne.jp>
	<20240626183311.05eaf091@rorschach.local.home>
	<6264da10-b6a0-40b8-ac26-c044b7f7529c@I-love.SAKURA.ne.jp>
	<20240626200906.37326e17@rorschach.local.home>
	<290aac9b-0664-404d-a457-292d69f9b22b@I-love.SAKURA.ne.jp>
X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu)
Precedence: bulk
X-Mailing-List: bpf@vger.kernel.org
List-Id: <bpf.vger.kernel.org>
List-Subscribe: <mailto:bpf+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:bpf+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Thu, 27 Jun 2024 09:21:38 +0900
Tetsuo Handa <penguin-kernel@I-love.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