linux-kernel - Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task

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Message-ID: <CAADnVQ+_TUjJ6Ytn96QqtHnBB--muefbbOoAsRw4z=40Pf1+tA@mail.gmail.com>
Date: Tue, 17 Dec 2024 15:49:53 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: syzbot <syzbot+97da3d7e0112d59971de@...kaller.appspotmail.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Eddy Z <eddyz87@...il.com>, Hao Luo <haoluo@...gle.com>, 
	John Fastabend <john.fastabend@...il.com>, Jiri Olsa <jolsa@...nel.org>, 
	KP Singh <kpsingh@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Matt Bobrowski <mattbobrowski@...gle.com>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Stanislav Fomichev <sdf@...ichev.me>, Song Liu <song@...nel.org>, 
	syzkaller-bugs <syzkaller-bugs@...glegroups.com>, Yonghong Song <yonghong.song@...ux.dev>
Subject: Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

On Mon, Dec 2, 2024 at 4:42 AM Puranjay Mohan <puranjay@...nel.org> wrote:
>
> Alexei Starovoitov <alexei.starovoitov@...il.com> writes:
>
> > Puranjay, Andrii and All,
> >
> > looks like if (irqs_disabled()) is not enough.
> > Should we change it to preemptible() ?
> >
> > It will likely make it async all the time,
> > but in this it's an ok trade off?
> >
>
> Yes, as BPF programs can run in all kinds of contexts.
>
> We should replace 'if (irqs_disabled())' with 'if (!preemptible())'
>
> because the definition is:
>
> #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
>
> and we need if ((preempt_count() != 0) || irqs_disabled()), in both
> these cases we want to make it async.
>
> I will try to test the fix as Syzbot has now found a reproducer.

Puranjay,

Any progress on a patch ?