Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending_irq() work on RT.

Arnaldo Carvalho de Melo
2024-03-13T13:28:44Z

On Wed, Mar 13, 2024 at 09:13:03AM +0100, Sebastian Andrzej Siewior wrote:
> On 2024-03-12 18:42:38 [-0300], Arnaldo Carvalho de Melo wrote:
> …
> > But:
> >
> > [acme@nine ~]$ pidof exec_child
> > 24273 24271 24270 24269 24268 24267 24266 24265 24264 24263 24262 24261 24260 24259
> …
>
> > [root@nine ~]# cat /proc/24263/stack
> > [<0>] irqentry_exit_to_user_mode+0x1c9/0x1e0
> > [<0>] asm_sysvec_apic_timer_interrupt+0x16/0x20
> > [root@nine ~]#
> …
> > [acme@nine ~]$ ps ax|grep exec_child| wc -l
> > 504
> > [acme@nine ~]$ 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@nine ~]$
> >
> > All in 'R' state.
> >
> > [root@nine ~]# killall exec_child
> > exec_child: no process found
> > [root@nine ~]# 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@nine ~]# kill 22964 23046 23128 23129 23181
> > [root@nine ~]# 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@nine ~]#

> You can't kill them?

I can, they remain in R state and I can kill them with 'kill `pidof exec_child`'

> > 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?

bare metal.

> 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.

> `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.

Checking that now, the stack is the one I posted:

> > [root@nine ~]# cat /proc/24263/stack
> > [<0>] irqentry_exit_to_user_mode+0x1c9/0x1e0
> > [<0>] asm_sysvec_apic_timer_interrupt+0x16/0x20
> > [root@nine ~]#

> I tried it on bare metal and VM and couldn't reproduce this.

All my tests are in bare metal.

- Arnaldo