linux-kernel - Re: [PATCH bpf] bpf: trace: send signals asynchronously if !preemptible

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Message-ID: <34f1132b-43de-44d2-9bc0-e25b49598711@linux.dev>
Date: Wed, 15 Jan 2025 08:55:30 -0800
From: Yonghong Song <yonghong.song@...ux.dev>
To: Puranjay Mohan <puranjay@...nel.org>, Song Liu <song@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>, KP Singh <kpsingh@...nel.org>,
 Matt Bobrowski <mattbobrowski@...gle.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, puranjay12@...il.com
Subject: Re: [PATCH bpf] bpf: trace: send signals asynchronously if
 !preemptible




On 1/15/25 2:36 AM, Puranjay Mohan wrote:
> BPF programs can execute in all kinds of contexts and when a program
> running in a non-preemptible context uses the bpf_send_signal() kfunc,
> it will cause issues because this kfunc can sleep.
>
> So change `irqs_disabled()` to `!preemptible()` that covers all edge
> cases: preempt_count() == 0 and irqs_disabled()
>
> Reported-by: syzbot+97da3d7e0112d59971de@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67486b09.050a0220.253251.0084.GAE@google.com/
> Fixes: 1bc7896e9ef4 ("bpf: Fix deadlock with rq_lock in bpf_send_signal()")
> Signed-off-by: Puranjay Mohan <puranjay@...nel.org>

Acked-by: Yonghong Song <yonghong.song@...ux.dev>