[v7,4/6] selftests/resctrl: Cleanup properly when an error occurs in CAT test

  After creating a child process with fork() in CAT test, if an error
occurs when parent process runs cat_val() or check_results(), the child
process will not be killed and also resctrlfs is not unmounted. Also if
an error occurs when child process runs cat_val() or check_results(),
the child process is returned, but the parent process will wait pipe
message from child.

Synchronize the exits between the parent and child. An error occurs
whether in parents process or child process, the parents process
always kills child process and runs umount_resctrlfs(), and the
child process always waits to be killed by the parent process.

Signed-off-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
---
 tools/testing/selftests/resctrl/cat_test.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)
  

On Mon, 13 Feb 2023, Shaopeng Tan wrote:

> After creating a child process with fork() in CAT test, if an error
> occurs when parent process runs cat_val() or check_results(), the child

I'd replace the rest of the paragraph with this:

"returns early. The parent will wait pipe message from child which will 
never be sent by the child and the parent cannot proceeed to unmount 
resctrlfs."

> process will not be killed and also resctrlfs is not unmounted. Also if
> an error occurs when child process runs cat_val() or check_results(),
> the child process is returned, but the parent process will wait pipe
> message from child.
>
> Synchronize the exits between the parent and child. An error occurs
> whether in parents process or child process, the parents process
> always kills child process and runs umount_resctrlfs(), and the
> child process always waits to be killed by the parent process.
> 
> Signed-off-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> ---
>  tools/testing/selftests/resctrl/cat_test.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 6a8306b0a109..477b62dac546 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -186,23 +186,20 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	remove(param.filename);
>  
>  	ret = cat_val(&param);
> -	if (ret)
> -		return ret;
> -
> -	ret = check_results(&param);
> -	if (ret)
> -		return ret;
> +	if (ret == 0)
> +		ret = check_results(&param);
>  
>  	if (bm_pid == 0) {
>  		/* Tell parent that child is ready */
>  		close(pipefd[0]);
>  		pipe_message = 1;
>  		if (write(pipefd[1], &pipe_message, sizeof(pipe_message)) <
> -		    sizeof(pipe_message)) {
> -			close(pipefd[1]);
> +		    sizeof(pipe_message))
> +			/*
> +			 * Just print the error message.
> +			 * Let while(1) run and wait for itself to be killed.
> +			 */
>  			perror("# failed signaling parent process");
> -			return errno;
> -		}
>  
>  		close(pipefd[1]);
>  		while (1)
> @@ -226,5 +223,5 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	if (bm_pid)
>  		umount_resctrlfs();
>  
> -	return 0;
> +	return ret;
>  }
> 

The code change looks good.
  

On 2/13/2023 2:00 AM, Ilpo Järvinen wrote:
> On Mon, 13 Feb 2023, Shaopeng Tan wrote:
> 
>> After creating a child process with fork() in CAT test, if an error
>> occurs when parent process runs cat_val() or check_results(), the child
> 
> I'd replace the rest of the paragraph with this:
> 
> "returns early. The parent will wait pipe message from child which will 
> never be sent by the child and the parent cannot proceeed to unmount 
> resctrlfs."

Note that the description is about an error within the parent process.
In the case snipped above it is the parent that exits early, not the child.
This first paragraph describes two scenarios, (a) error in parent, and (b)
error in child. I think it is good information to keep descriptions of
both scenarios.

The proposed addition could be used to expand the description of the scenario
when an error occurs in the child. In this case please consider changing "wait
pipe message from child" to "wait for the pipe message from the child", and
"proceeed" to "proceed".

Reinette
  

Hi Shaopeng,

On 2/12/2023 10:24 PM, Shaopeng Tan wrote:
> After creating a child process with fork() in CAT test, if an error
> occurs when parent process runs cat_val() or check_results(), the child
> process will not be killed and also resctrlfs is not unmounted. Also if
> an error occurs when child process runs cat_val() or check_results(),
> the child process is returned, but the parent process will wait pipe

"child process is returned" -> "child process returns"

> message from child.

"will wait pipe message from child" -> "will wait for the pipe message
from the child"

> Synchronize the exits between the parent and child. An error occurs
> whether in parents process or child process, the parents process
> always kills child process and runs umount_resctrlfs(), and the
> child process always waits to be killed by the parent process.

I think the above could be easier to read with a few slight changes:

"
Synchronize the exits between the parent and child. An error could
occur whether in parent process or child process. The parent process
always kills the child process and runs umount_resctrlfs(). The
child process always waits to be killed by the parent process."


> 
> Signed-off-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> ---
>  tools/testing/selftests/resctrl/cat_test.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 6a8306b0a109..477b62dac546 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -186,23 +186,20 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	remove(param.filename);
>  
>  	ret = cat_val(&param);
> -	if (ret)
> -		return ret;
> -
> -	ret = check_results(&param);
> -	if (ret)
> -		return ret;
> +	if (ret == 0)
> +		ret = check_results(&param);
>  
>  	if (bm_pid == 0) {
>  		/* Tell parent that child is ready */
>  		close(pipefd[0]);
>  		pipe_message = 1;
>  		if (write(pipefd[1], &pipe_message, sizeof(pipe_message)) <
> -		    sizeof(pipe_message)) {
> -			close(pipefd[1]);
> +		    sizeof(pipe_message))
> +			/*
> +			 * Just print the error message.
> +			 * Let while(1) run and wait for itself to be killed.
> +			 */
>  			perror("# failed signaling parent process");
> -			return errno;
> -		}
>  
>  		close(pipefd[1]);
>  		while (1)
> @@ -226,5 +223,5 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	if (bm_pid)
>  		umount_resctrlfs();
>  
> -	return 0;
> +	return ret;
>  }

Apart from the changelog comments:

Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Thank you very much

Reinette
  

On Mon, 13 Feb 2023, Reinette Chatre wrote:

> 
> 
> On 2/13/2023 2:00 AM, Ilpo Järvinen wrote:
> > On Mon, 13 Feb 2023, Shaopeng Tan wrote:
> > 
> >> After creating a child process with fork() in CAT test, if an error
> >> occurs when parent process runs cat_val() or check_results(), the child
> > 
> > I'd replace the rest of the paragraph with this:
> > 
> > "returns early. The parent will wait pipe message from child which will 
> > never be sent by the child and the parent cannot proceeed to unmount 
> > resctrlfs."
> 
> Note that the description is about an error within the parent process.
> In the case snipped above it is the parent that exits early, not the child.

Ah, that a good point. Somehow I was too fixed into thinking the child 
exiting because it's what it's come across myself.