linux-kernel - Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending

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Message-ID: <20240313081303.DClwQrvb@linutronix.de>
Date: Wed, 13 Mar 2024 09:13:03 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ian Rogers <irogers@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>, Marco Elver <elver@...gle.com>,
	Mark Rutland <mark.rutland@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending_irq() work
 on RT.

On 2024-03-12 18:42:38 [-0300], Arnaldo Carvalho de Melo wrote:
…
> But:
> 
> [acme@...e ~]$ pidof exec_child
> 24273 24271 24270 24269 24268 24267 24266 24265 24264 24263 24262 24261 24260 24259 
…

> [root@...e ~]# cat /proc/24263/stack
> [<0>] irqentry_exit_to_user_mode+0x1c9/0x1e0
> [<0>] asm_sysvec_apic_timer_interrupt+0x16/0x20
> [root@...e ~]#
…
> [acme@...e ~]$ ps ax|grep exec_child| wc -l
> 504
> [acme@...e ~]$ ps ax|grep exec_child| tail
>   24264 pts/0    R      0:04 exec_child
>   24265 pts/0    R      0:04 exec_child
>   24266 pts/0    R      0:04 exec_child
>   24267 pts/0    R      0:04 exec_child
>   24268 pts/0    R      0:04 exec_child
>   24269 pts/0    R      0:04 exec_child
>   24270 pts/0    R      0:04 exec_child
>   24271 pts/0    R      0:04 exec_child
>   24273 pts/0    R      0:04 exec_child
>   26704 pts/1    S+     0:00 grep --color=auto exec_child
> [acme@...e ~]$
> 
> All in 'R' state.
> 
> [root@...e ~]# killall exec_child
> exec_child: no process found
> [root@...e ~]# ps ax | grep exec_child | head -5
>   22964 pts/0    R      0:06 exec_child
>   23046 pts/0    R      0:05 exec_child
>   23128 pts/0    R      0:05 exec_child
>   23129 pts/0    R      0:05 exec_child
>   23181 pts/0    R      0:05 exec_child
> [root@...e ~]# kill 22964 23046 23128 23129 23181
> [root@...e ~]# ps ax | grep exec_child | head -5
>   23182 pts/0    R      0:06 exec_child
>   23196 pts/0    R      0:06 exec_child
>   23197 pts/0    R      0:06 exec_child
>   23210 pts/0    R      0:06 exec_child
>   23213 pts/0    R      0:06 exec_child
> [root@...e ~]#

You can't kill them?

> at the end they disappeared, on this last run.
> 
> But if I do a 'killall remove_on_exec' and stop that loop (control+C/Z)
> we get all those exec_child running a seemingly eternal loop:

Is this new or was it there? Is this VM or bare metal?

One part I don't get: did you let it run or did you kill it?
`exec_child' spins until a signal is received or the parent kills it. So
it shouldn't remain there for ever. And my guess, that it is in spinning
in userland and not in kernel.
I tried it on bare metal and VM and couldn't reproduce this.
…
> 
> - Arnaldo

Sebastian