linux-kernel - Re: WARNING in bpf_bprintf

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Date:   Tue, 15 Nov 2022 18:01:15 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Hao Sun <sunhao.th@...il.com>
Cc:     Jiri Olsa <olsajiri@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Hao Luo <haoluo@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Stanislav Fomichev <sdf@...gle.com>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>
Subject: Re: WARNING in bpf_bprintf_prepare

On Tue, Nov 15, 2022 at 09:48:27AM +0800, Hao Sun wrote:

SNIP

> > > > Hi Jirka,
> > > >
> > > > I've tested the proposed patch, the warning from bpf_bprintf_prepare will not
> > > > be triggered with the patch, but the reproducer can still trigger the following
> > > > warning. My test was conducted on:
> > > >
> > > > commit:  f67dd6ce0723 Merge tag 'slab-for-6.1-rc4-fixes'
> > > > git tree:   upstream
> > > > kernel config: https://pastebin.com/raw/sE5QK5HL
> > > > C reproducer: https://pastebin.com/raw/X96ASi27
> > > > console log *before* the patch: https://pastebin.com/raw/eSCUNFrd
> > > > console log *after* the patch: https://pastebin.com/raw/tzcmdWZt
> > >
> > > thanks for testing.. I can't reproduce this for some reason
> > >
> > > I'll check some more and perhaps go with denying bpf attachment
> > > for this tracepoint as Alexei suggeste
> >
> > the change below won't allow to attach bpf program with any printk
> > helper in contention_begin and bpf_trace_printk tracepoints
> >
> > I still need to test it on the machine that reproduced the issue
> > for me.. meanwhile any feedback is appreciated
> >
> 
> Hi,
> 
> Tested on my machine, the C reproducer won't trigger any issue
> this time with the patch. The test was conducted on:
> 
> commit:  f67dd6ce0723 Merge tag 'slab-for-6.1-rc4-fixes'
> git tree:   upstream
> kernel config: https://pastebin.com/raw/sE5QK5HL
> C reproducer: https://pastebin.com/raw/X96ASi27
> full console log *before* the patch: https://pastebin.com/raw/n3x55RDr
> full console log *after* the patch: https://pastebin.com/raw/7HdxnCnL

thanks, looks good on my end as well

jirka