linux-kernel - Re: [RFC PATCH v2 12/12] rv: Add opid per-cpu monitor

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Message-ID: <20250527133712.CFW5AcNE@linutronix.de>
Date: Tue, 27 May 2025 15:37:12 +0200
From: Nam Cao <namcao@...utronix.de>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tomas Glozar <tglozar@...hat.com>, Juri Lelli <jlelli@...hat.com>
Subject: Re: [RFC PATCH v2 12/12] rv: Add opid per-cpu monitor

On Wed, May 14, 2025 at 10:43:14AM +0200, Gabriele Monaco wrote:
> Add a per-cpu monitor as part of the sched model:
> * opid: operations with preemption and irq disabled
>     Monitor to ensure wakeup and need_resched occur with irq and
>     preemption disabled or in irq handlers.

This monitor reports some warnings:

$ perf record -e rv:error_opid --call-graph dwarf -a -- ./stress-epoll
(stress-epoll program from
https://github.com/rouming/test-tools/blob/master/stress-epoll.c)

$ perf script
stress-epoll   315 [003]   527.674724: rv:error_opid: event preempt_disable not expected in the state preempt_disabled
	ffffffff9fdfb34f da_event_opid+0x10f ([kernel.kallsyms])
	ffffffff9fdfb34f da_event_opid+0x10f ([kernel.kallsyms])
	ffffffff9fdfba0d handle_preempt_disable+0x3d ([kernel.kallsyms])
	ffffffff9fdd32d0 __traceiter_preempt_disable+0x30 ([kernel.kallsyms])
	ffffffff9fdd38fe trace_preempt_off+0x4e ([kernel.kallsyms])
	ffffffff9fee6c1c vfs_write+0x12c ([kernel.kallsyms])
	ffffffff9fee7128 ksys_write+0x68 ([kernel.kallsyms])
	ffffffffa0bdbd92 do_syscall_64+0xb2 ([kernel.kallsyms])
	ffffffff9fa00130 entry_SYSCALL_64_after_hwframe+0x77 ([kernel.kallsyms])
	           f833f __GI___libc_write+0x4f (/usr/lib/x86_64-linux-gnu/libc.so.6)
	           f833f __GI___libc_write+0x4f (/usr/lib/x86_64-linux-gnu/libc.so.6)
	            1937 thread_work+0x47 (/root/test-tools/stress-epoll)
	           891f4 start_thread+0x304 (/usr/lib/x86_64-linux-gnu/libc.so.6)
	          10989b clone3+0x2b (/usr/lib/x86_64-linux-gnu/libc.so.6)

stress-epoll   318 [002]   527.674759: rv:error_opid: event preempt_disable not expected in the state disabled
	ffffffff9fdfb34f da_event_opid+0x10f ([kernel.kallsyms])
	ffffffff9fdfb34f da_event_opid+0x10f ([kernel.kallsyms])
	ffffffff9fdfba0d handle_preempt_disable+0x3d ([kernel.kallsyms])
	ffffffff9fdd32d0 __traceiter_preempt_disable+0x30 ([kernel.kallsyms])
	ffffffff9fdd38fe trace_preempt_off+0x4e ([kernel.kallsyms])
	ffffffffa0bec1aa _raw_spin_lock_irq+0x1a ([kernel.kallsyms])
	ffffffff9ff4fe73 eventfd_write+0x63 ([kernel.kallsyms])
	ffffffff9fee6be5 vfs_write+0xf5 ([kernel.kallsyms])
	ffffffff9fee7128 ksys_write+0x68 ([kernel.kallsyms])
	ffffffffa0bdbd92 do_syscall_64+0xb2 ([kernel.kallsyms])
	ffffffff9fa00130 entry_SYSCALL_64_after_hwframe+0x77 ([kernel.kallsyms])
	           f833f __GI___libc_write+0x4f (/usr/lib/x86_64-linux-gnu/libc.so.6)
	           f833f __GI___libc_write+0x4f (/usr/lib/x86_64-linux-gnu/libc.so.6)
	            1937 thread_work+0x47 (/root/test-tools/stress-epoll)
	           891f4 start_thread+0x304 (/usr/lib/x86_64-linux-gnu/libc.so.6)
	          10989b clone3+0x2b (/usr/lib/x86_64-linux-gnu/libc.so.6)

I'm not sure what I'm looking at here. Do you think these are kernel bugs,
or the monitor is missing some corner cases?

Best regards,
Nam