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

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Date: Wed, 13 Mar 2024 14:46:45 +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 2024-03-13 10:28:41 [-0300], Arnaldo Carvalho de Melo wrote:
> > One part I don't get: did you let it run or did you kill it?
> 
> If I let them run they will finish and exit, no exec_child remains.
> 
> If I instead try to stop the loop that goes on forking the 100 of them,
> then the exec_child remain spinning.

Okay. So that problem only exists if you intervene. And you can
reproduce this odd behaviour with my patches but not without them,
right?

> > it shouldn't remain there for ever. And my guess, that it is in spinning
> > in userland and not in kernel.
> 
> Checking that now, the stack is the one I posted:
> 
> > > [root@...e ~]# cat /proc/24263/stack
> > > [<0>] irqentry_exit_to_user_mode+0x1c9/0x1e0
> > > [<0>] asm_sysvec_apic_timer_interrupt+0x16/0x20
> > > [root@...e ~]#

could you resolve irqentry_exit_to_user_mode+0x1c9/0x1e0, please?

> > I tried it on bare metal and VM and couldn't reproduce this.
> 
> All my tests are in bare metal.

Would you mind sending me your .config? The shell is bash I guess. I
will try to reproduce your setup on another box…

> - Arnaldo

Sebastian