From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
bpf@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [PATCH v6 0/3] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast
Date: Mon, 26 Jan 2026 21:39:22 -0500 [thread overview]
Message-ID: <20260126213922.0a91bfac@robin> (raw)
In-Reply-To: <20260126231145.728172709@kernel.org>
On Mon, 26 Jan 2026 18:11:45 -0500
Steven Rostedt <rostedt@kernel.org> wrote:
> The current use of guard(preempt_notrace)() within __DECLARE_TRACE()
> to protect invocation of __DO_TRACE_CALL() means that BPF programs
> attached to tracepoints are non-preemptible. This is unhelpful in
> real-time systems, whose users apparently wish to use BPF while also
> achieving low latencies.
>
> Change the protection of tracepoints to use fast_srcu() instead.
> This will allow the callbacks to be able to be preempted. This also
> means that the callbacks themselves need to be able to handle this
> new found preemption ability.
>
> For perf, add a guard(preempt) inside its handler too keep the old behavior
> of perf events being called with preemption disabled.
>
> For BPF, add a migrate_disable() to its handler. Actually, just replace
> the rcu_read_lock() with rcu_read_lock_dont_migrate() and make it
> cover more of the BPF callback handler.
My tests just triggered this, so I'm removing them from my queue for now.
-- Steve
[ 204.194772] ------------[ cut here ]------------
[ 204.194789] WARNING: kernel/rcu/srcutree.c:792 at __srcu_check_read_flavor+0x5c/0xb0, CPU#1: swapper/1/0
[ 204.194800] Modules linked in:
[ 204.194817] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.19.0-rc7-test-00018-g2c774d6ad074-dirty #32 PREEMPT(voluntary)
[ 204.194821] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 204.194824] RIP: 0010:__srcu_check_read_flavor+0x5c/0xb0
[ 204.194829] Code: 84 c9 74 19 39 f1 74 45 0f 0b 85 c0 74 2e 39 c1 74 45 0f 0b 39 f0 75 3f c3 cc cc cc cc 85 c0 74 16 83 fe 04 75 ee 0f 0b eb ea <0f> 0b 8d 46 ff 85 f0 74 ba 0f 0b eb b6 83
fe 04 74 3a 31 c0 f0 0f
[ 204.194832] RSP: 0018:fffffe4c48325b50 EFLAGS: 00010002
[ 204.194835] RAX: 0000000000000001 RBX: ffffffff8791e5a0 RCX: 0000000000000000
[ 204.194836] RDX: 00000000ffffffff RSI: 0000000000000004 RDI: ffffffff879f1180
[ 204.194838] RBP: ffff8e6453fd2000 R08: 0000000000000001 R09: 0000000000000000
[ 204.194839] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
[ 204.194840] R13: fffffe4c48325ef8 R14: ffffffff85eeae93 R15: ffff8e6453906900
[ 204.194842] FS: 0000000000000000(0000) GS:ffff8e6533593000(0000) knlGS:0000000000000000
[ 204.194844] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 204.194845] CR2: 000055d1e7cf8cc0 CR3: 000000010b0cc004 CR4: 0000000000172ef0
[ 204.194850] Call Trace:
[ 204.194866] <NMI>
[ 204.194868] lock_release+0x215/0x320
[ 204.194886] ? arch_perf_update_userpage+0x6c/0xf0
[ 204.195214] perf_event_update_userpage+0x158/0x2e0
[ 204.195538] x86_perf_event_set_period+0xc1/0x180
[ 204.195811] handle_pmi_common+0x1ac/0x450
[ 204.198605] ? __get_next_timer_interrupt+0x185/0x370
[ 204.198914] intel_pmu_handle_irq+0x10e/0x510
[ 204.199032] ? nmi_handle.part.0+0x30/0x270
[ 204.199197] ? __get_next_timer_interrupt+0x185/0x370
[ 204.199404] perf_event_nmi_handler+0x34/0x60
[ 204.199523] nmi_handle.part.0+0xc9/0x270
next prev parent reply other threads:[~2026-01-27 2:39 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-26 23:11 [PATCH v6 0/3] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast Steven Rostedt
2026-01-26 23:11 ` [PATCH v6 1/3] tracing: perf: Have perf tracepoint callbacks always disable preemption Steven Rostedt
2026-01-26 23:11 ` [PATCH v6 2/3] bpf: Have __bpf_trace_run() use rcu_read_lock_dont_migrate() Steven Rostedt
2026-01-26 23:11 ` [PATCH v6 3/3] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast Steven Rostedt
2026-01-27 2:39 ` Steven Rostedt [this message]
2026-01-27 23:18 ` [PATCH v6 0/3] " Paul E. McKenney
2026-01-30 0:33 ` Steven Rostedt
2026-01-30 1:32 ` Paul E. McKenney
2026-01-30 2:50 ` Steven Rostedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260126213922.0a91bfac@robin \
--to=rostedt@goodmis.org \
--cc=akpm@linux-foundation.org \
--cc=ast@kernel.org \
--cc=bigeasy@linutronix.de \
--cc=bpf@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mhiramat@kernel.org \
--cc=paulmck@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox