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

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

[Kajol Jain]

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.

Fixes: 2ed6edd33a21("perf: Add cond_resched() to task_function_call()")
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reviewed-by: Barret Rhoden <brho@google.com>
Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 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

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@linux.ibm.com>
> Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reviewed-by: Barret Rhoden <brho@google.com>
> Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  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

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

[kajoljain]

On 9/2/20 8:35 PM, Arnaldo Carvalho de Melo wrote:
> 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:

Hi Arnaldo,
    You are right, once we bring back the CPU again, things will start working as our 'smp_call_function_single'
will not fail and we will come out of the loop. But till then, task_function_call will be hung.

Thanks,
Kajol Jain
> 
> [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@linux.ibm.com>
>> Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> Reviewed-by: Barret Rhoden <brho@google.com>
>> Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> ---
>>  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
>>
> 

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

[kajoljain]

On 8/27/20 12:17 PM, Kajol Jain wrote:
> 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.

Hi Peter,
     Please let me know if you have any comment on this patch.

Thanks,
Kajol Jain
> 
> Fixes: 2ed6edd33a21("perf: Add cond_resched() to task_function_call()")
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
> Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reviewed-by: Barret Rhoden <brho@google.com>
> Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  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;
> 

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

[Peter Zijlstra]

On Thu, Oct 08, 2020 at 05:55:35PM +0530, kajoljain wrote:
> 
> 
> On 8/27/20 12:17 PM, Kajol Jain wrote:
> > 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.
> 
> Hi Peter,
>      Please let me know if you have any comment on this patch.

Yes, sorry. I've got it now. Thanks!

---
Subject: perf: Fix task_function_call() error handling
From: Kajol Jain <kjain@linux.ibm.com>
Date: Thu, 27 Aug 2020 12:17:32 +0530

From: Kajol Jain <kjain@linux.ibm.com>

The error handling introduced by commit:

  2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")

looses any return value from smp_call_function_single() that is not
{0, -EINVAL}. This is a problem because it will return -EXNIO when the
target CPU is offline. Worse, in that case it'll turn into an infinite
loop.

Fixes: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")
Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Barret Rhoden <brho@google.com>
Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: https://lkml.kernel.org/r/20200827064732.20860-1-kjain@linux.ibm.com
---
 kernel/events/core.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- 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
 	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;

[tip: perf/core] perf: Fix task_function_call() error handling

[tip-bot2 for Kajol Jain]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     84ad70320241566e028ada955c694ab92f3351e3
Gitweb:        https://git.kernel.org/tip/84ad70320241566e028ada955c694ab92f3351e3
Author:        Kajol Jain <kjain@linux.ibm.com>
AuthorDate:    Thu, 27 Aug 2020 12:17:32 +05:30
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 08 Oct 2020 15:16:29 +02:00

perf: Fix task_function_call() error handling

The error handling introduced by commit:

  2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")

looses any return value from smp_call_function_single() that is not
{0, -EINVAL}. This is a problem because it will return -EXNIO when the
target CPU is offline. Worse, in that case it'll turn into an infinite
loop.

Fixes: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")
Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Barret Rhoden <brho@google.com>
Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: https://lkml.kernel.org/r/20200827064732.20860-1-kjain@linux.ibm.com
---
 kernel/events/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 45edb85..85a6e7f 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;

[tip: perf/urgent] perf: Fix task_function_call() error handling

[tip-bot2 for Kajol Jain]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     6d6b8b9f4fceab7266ca03d194f60ec72bd4b654
Gitweb:        https://git.kernel.org/tip/6d6b8b9f4fceab7266ca03d194f60ec72bd4b654
Author:        Kajol Jain <kjain@linux.ibm.com>
AuthorDate:    Thu, 27 Aug 2020 12:17:32 +05:30
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 09 Oct 2020 08:18:33 +02:00

perf: Fix task_function_call() error handling

The error handling introduced by commit:

  2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")

looses any return value from smp_call_function_single() that is not
{0, -EINVAL}. This is a problem because it will return -EXNIO when the
target CPU is offline. Worse, in that case it'll turn into an infinite
loop.

Fixes: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()")
Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Barret Rhoden <brho@google.com>
Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: https://lkml.kernel.org/r/20200827064732.20860-1-kjain@linux.ibm.com
---
 kernel/events/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7ed5248..e8bf922 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;