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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Tue, 19 Mar 2024 23:56:31 -0700
Message-ID: <CAADnVQLmLMt2bF9aAB26dtBCvy2oUFt+AAKDRgTTrc7Xk_zxJQ@mail.gmail.com>
Subject: Re: [syzbot] [kernel?] possible deadlock in console_flush_all (2)
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: syzbot <syzbot+f78380e4eae53c64125c@syzkaller.appspotmail.com>, 
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, John Fastabend <john.fastabend@gmail.com>, 
	Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>, 
	John Ogness <john.ogness@linutronix.de>, Sergey Senozhatsky <senozhatsky@chromium.org>, 
	Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>, 
	bpf <bpf@vger.kernel.org>
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On Tue, Mar 19, 2024 at 11:50=E2=80=AFPM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Hello, bpf developers.
>
> syzbot is reporting circular locking dependency because bpf program is hi=
tting
> printk() path. To avoid this dependency, something like
> https://syzkaller.appspot.com/text?tag=3DPatch&x=3D121c92fe180000 is need=
ed.
>
> Is it possible to call printk_deferred_{enter,exit}() from the bpf side (=
e.g.
> bpf_prog_run()) so that we don't need to add overhead on the scheduler si=
de
> when bpf programs are not registered?
>
> printk_deferred_{enter,exit}() requires that printk_deferred_exit() is ca=
lled
> on a CPU which printk_deferred_enter() was called, for percpu counter is =
used.
> Is migrate_{disable,enable}() also needed around printk_deferred_{enter,e=
xit}() ?
>
> On 2023/10/08 15:28, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    7d730f1bf6f3 Add linux-next specific files for 20231005
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=3D172d36e9680=
000

This has nothing to do with bpf.
bpf never calls printk().