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From: Puranjay Mohan <puranjay@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: syzbot <syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com>, 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
In-Reply-To: <CAADnVQL=_6n+yJfs+TPxtBEVcpYV6nPEgjfRmacCdm7qLCSj0g@mail.gmail.com>
References: <67486b09.050a0220.253251.0084.GAE@google.com>
 <CAADnVQKdRWA1zG6X4XNwOWtKiUHN-SRREYN_DCNU59LsK8S5LA@mail.gmail.com>
 <mb61p8qsymf3i.fsf@kernel.org>
 <CAADnVQ+_TUjJ6Ytn96QqtHnBB--muefbbOoAsRw4z=40Pf1+tA@mail.gmail.com>
 <CAADnVQL=_6n+yJfs+TPxtBEVcpYV6nPEgjfRmacCdm7qLCSj0g@mail.gmail.com>
Date: Wed, 15 Jan 2025 10:38:56 +0000
Message-ID: <mb61p5xmgicov.fsf@kernel.org>
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Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Tue, Dec 17, 2024 at 3:49=E2=80=AFPM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>>
>> On Mon, Dec 2, 2024 at 4:42=E2=80=AFAM Puranjay Mohan <puranjay@kernel.o=
rg> wrote:
>> >
>> > 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() =3D=3D 0 && !irqs_disabled())
>> >
>> > and we need if ((preempt_count() !=3D 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 ?
>
> ping.

Hi Alexei,
Sorry for being AWOL. I was on a long vacation in India and just got
back.

Here is the patch to fix this: https://lore.kernel.org/all/20250115103647.3=
8487-1-puranjay@kernel.org/

Thanks,
Puranjay

#syz test: https://github.com/puranjaymohan/bpf.git bpf_preemt_fix

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