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From: Puranjay Mohan <puranjay@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	syzbot <syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Eddy Z <eddyz87@gmail.com>, Hao Luo <haoluo@google.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Jiri Olsa <jolsa@kernel.org>, KP Singh <kpsingh@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-trace-kernel <linux-trace-kernel@vger.kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Matt Bobrowski <mattbobrowski@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Stanislav Fomichev <sdf@fomichev.me>, Song Liu <song@kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Yonghong Song <yonghong.song@linux.dev>
Subject: Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand
Date: Mon, 02 Dec 2024 12:41:53 +0000	[thread overview]
Message-ID: <mb61p8qsymf3i.fsf@kernel.org> (raw)
In-Reply-To: <CAADnVQKdRWA1zG6X4XNwOWtKiUHN-SRREYN_DCNU59LsK8S5LA@mail.gmail.com>

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Alexei Starovoitov <alexei.starovoitov@gmail.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.

Thanks,
Puranjay

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  reply	other threads:[~2024-12-02 12:42 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-11-28 13:07 [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand syzbot
2024-11-29 16:47 ` Alexei Starovoitov
2024-12-02 12:41   ` Puranjay Mohan [this message]
2024-12-17 23:49     ` Alexei Starovoitov
2024-12-20 17:30       ` Alexei Starovoitov
2025-01-15 10:38         ` Puranjay Mohan
2025-01-15 11:47           ` syzbot
2024-12-02 10:14 ` syzbot

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