Re: [PATCH] perf/core: Fix hung issue on perf stat command during cpu hotplug

[Arnaldo Carvalho de Melo]

Em Thu, Aug 27, 2020 at 12:17:32PM +0530, Kajol Jain escreveu:
> Commit 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")
> added assignment of ret value as -EAGAIN in case function
> call to 'smp_call_function_single' fails.
> For non-zero ret value, it did
> 'ret = !ret ? data.ret : -EAGAIN;', which always
> assign -EAGAIN to ret and make second if condition useless.
> 
> In scenarios like when executing a perf stat with --per-thread option, and
> if any of the monitoring cpu goes offline, the 'smp_call_function_single'
> function could return -ENXIO, and with the above check,
> task_function_call hung and increases CPU
> usage (because of repeated 'smp_call_function_single()')
> 
> Recration scenario:
> 	# perf stat -a --per-thread && (offline a CPU )
> 
> Patch here removes the tertiary condition added as part of that
> commit and added a check for NULL and -EAGAIN.

I reproduced this issue with v5.9-rc3, now have to reboot for a conf
call, will try to test the patch afterwards,

[65108.467416] IRQ 165: no longer affine to CPU23
[65108.468495] smpboot: CPU 23 is now offline
[65129.003879] Uhhuh. NMI received for unknown reason 1c on CPU 20.
[65129.003880] Do you have a strange power saving mode enabled?
[65129.003880] Dazed and confused, but trying to continue
[65156.155539] Uhhuh. NMI received for unknown reason 1c on CPU 2.
[65156.155539] Do you have a strange power saving mode enabled?
[65156.155540] Dazed and confused, but trying to continue
[65161.985284] Uhhuh. NMI received for unknown reason 1c on CPU 21.
[65161.985285] Do you have a strange power saving mode enabled?
[65161.985285] Dazed and confused, but trying to continue
[65183.154444] Uhhuh. NMI received for unknown reason 1c on CPU 1.
[65183.154445] Do you have a strange power saving mode enabled?
[65183.154446] Dazed and confused, but trying to continue
[65189.724797] Uhhuh. NMI received for unknown reason 0c on CPU 4.
[65189.724798] Do you have a strange power saving mode enabled?
[65189.724799] Dazed and confused, but trying to continue
[65196.259918] Uhhuh. NMI received for unknown reason 1c on CPU 11.
[65196.259918] Do you have a strange power saving mode enabled?
[65196.259918] Dazed and confused, but trying to continue
[65234.794490] Uhhuh. NMI received for unknown reason 0c on CPU 5.
[65234.794491] Do you have a strange power saving mode enabled?
[65234.794491] Dazed and confused, but trying to continue
[65454.559831] Uhhuh. NMI received for unknown reason 1c on CPU 19.
[65454.559832] Do you have a strange power saving mode enabled?
[65454.559832] Dazed and confused, but trying to continue
[65529.657789] Uhhuh. NMI received for unknown reason 1c on CPU 3.
[65529.657790] Do you have a strange power saving mode enabled?
[65529.657790] Dazed and confused, but trying to continue
[acme@five perf]$


Things seems to be working again after bringing that CPU back online:

[root@five ~]# perf top --stdio -C 0-22
Error:
The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles).
/bin/dmesg | grep -i perf may provide additional information.

[root@five ~]# perf stat -e cycles sleep 1
Error:
The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles).
/bin/dmesg | grep -i perf may provide additional information.

[root@five ~]# perf record -e cycles sleep 1
Error:
The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles).
/bin/dmesg | grep -i perf may provide additional information.

[root@five ~]# echo 1 > /sys/devices/system/cpu/cpu23/online
[root@five ~]# perf record -e cycles sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.039 MB perf.data (7 samples) ]
[root@five ~]# perf stat -e cycles sleep 1

 Performance counter stats for 'sleep 1':

           842,743      cycles

       1.000903853 seconds time elapsed

       0.000902000 seconds user
       0.000000000 seconds sys


[root@five ~]# perf stat -e cycles sleep 1


- Arnaldo

 
> Fixes: 2ed6edd33a21("perf: Add cond_resched() to task_function_call()")
> Signed-off-by: Kajol Jain <kjain@xxxxxxxxxxxxx>
> Reported-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Barret Rhoden <brho@xxxxxxxxxx>
> Tested-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> ---
>  kernel/events/core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Changelog:
> - Remove RFC tag
> - Resolve some nits issues like space after if and
>   added -ENXIO in comment msg of function 'task_function_call'
>   as suggested by Barret Rhoden.
> 
> Link to the RFC: https://lkml.org/lkml/2020/8/26/896
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5bfe8e3c6e44..cef646084198 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -99,7 +99,7 @@ static void remote_function(void *data)
>   * retry due to any failures in smp_call_function_single(), such as if the
>   * task_cpu() goes offline concurrently.
>   *
> - * returns @func return value or -ESRCH when the process isn't running
> + * returns @func return value or -ESRCH or -ENXIO when the process isn't running
>   */
>  static int
>  task_function_call(struct task_struct *p, remote_function_f func, void *info)
> @@ -115,7 +115,8 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info)
>  	for (;;) {
>  		ret = smp_call_function_single(task_cpu(p), remote_function,
>  					       &data, 1);
> -		ret = !ret ? data.ret : -EAGAIN;
> +		if (!ret)
> +			ret = data.ret;
>  
>  		if (ret != -EAGAIN)
>  			break;
> -- 
> 2.26.2
> 

-- 

- Arnaldo