linux-kernel - Re: [PATCH] bpf: use raw_spinlock

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Message-ID: <a22858d6-1676-4429-b617-86191e44cb65@iogearbox.net>
Date: Tue, 24 Sep 2024 18:46:10 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Wander Lairson Costa <wander@...hat.com>,
 Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, "open list:BPF [RINGBUF]"
 <bpf@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Cc: Wander Lairson Costa <wander.lairson@...il.com>,
 Brian Grech <bgrech@...hat.com>
Subject: Re: [PATCH] bpf: use raw_spinlock_t in ringbuf

On 9/20/24 9:06 PM, Wander Lairson Costa wrote:
> From: Wander Lairson Costa <wander.lairson@...il.com>
>
> The function __bpf_ringbuf_reserve is invoked from a tracepoint, which
> disables preemption. Using spinlock_t in this context can lead to a
> "sleep in atomic" warning in the RT variant. This issue is illustrated
> in the example below:
>
> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 556208, name: test_progs
> preempt_count: 1, expected: 0
> RCU nest depth: 1, expected: 1
> INFO: lockdep is turned off.
> Preemption disabled at:
> [<ffffd33a5c88ea44>] migrate_enable+0xc0/0x39c
> CPU: 7 PID: 556208 Comm: test_progs Tainted: G
> Hardware name: Qualcomm SA8775P Ride (DT)
> Call trace:
>   dump_backtrace+0xac/0x130
>   show_stack+0x1c/0x30
>   dump_stack_lvl+0xac/0xe8
>   dump_stack+0x18/0x30
>   __might_resched+0x3bc/0x4fc
>   rt_spin_lock+0x8c/0x1a4
>   __bpf_ringbuf_reserve+0xc4/0x254
>   bpf_ringbuf_reserve_dynptr+0x5c/0xdc
>   bpf_prog_ac3d15160d62622a_test_read_write+0x104/0x238
>   trace_call_bpf+0x238/0x774
>   perf_call_bpf_enter.isra.0+0x104/0x194
>   perf_syscall_enter+0x2f8/0x510
>   trace_sys_enter+0x39c/0x564
>   syscall_trace_enter+0x220/0x3c0
>   do_el0_svc+0x138/0x1dc
>   el0_svc+0x54/0x130
>   el0t_64_sync_handler+0x134/0x150
>   el0t_64_sync+0x17c/0x180
>
> Switch the spinlock to raw_spinlock_t to avoid this error.
>
> Signed-off-by: Wander Lairson Costa <wander.lairson@...il.com>
> Reported-by: Brian Grech <bgrech@...hat.com>
> Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
> Signed-off-by: Wander Lairson Costa <wander@...hat.com>
Fix is for bpf tree, lgtm:

Acked-by: Daniel Borkmann <daniel@...earbox.net>