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

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Message-ID: <744c9c43-9e4f-4069-9773-067036237bff@I-love.SAKURA.ne.jp>
Date: Wed, 26 Jun 2024 09:02:22 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: 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>, Steven Rostedt <rostedt@...dmis.org>,
        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 2024/06/26 8:56, Alexei Starovoitov wrote:
> You are missing the point. The bug has nothing to do with bpf.

The bug is caused by calling tracing hooks with rq lock held.
If tracing hooks do not exist, this bug does not exist.

> It can happen without any bpf loaded. Exactly the same way.
> should_fail_usercopy() is called on all user accesses.

Not all callers of e.g. should_fail_usercopy() are holding rq lock.