linux-kernel - RE: [PATCH v4 4/5] selftests/resctrl: Cleanup properly when an error occurs in CAT test

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Message-ID: <TYAPR01MB6330CDB2C59C58EE77B912538B0F9@TYAPR01MB6330.jpnprd01.prod.outlook.com>
Date:   Thu, 24 Nov 2022 08:17:34 +0000
From:   "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>
To:     'Reinette Chatre' <reinette.chatre@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: RE: [PATCH v4 4/5] selftests/resctrl: Cleanup properly when an error
 occurs in CAT test

Hi Reinette,

> On 11/16/2022 5:05 PM, Shaopeng Tan wrote:
> > After creating a child process with fork() in CAT test, if there is
> > an error occurs or such as a SIGINT signal is received, the parent
> > process will be terminated immediately, but the child process will not
> > be killed and also umount_resctrlfs() will not be called.
> >
> > Add a signal handler like other tests to kill child process, umount
> > resctrlfs, cleanup result files, etc. if an error occurs in parent
> > process. To use ctrlc_handler() of other tests to kill child
> > process(bm_pid), using global bm_pid instead of local bm_pid.
> >
> > Wait for child process to be killed if an error occurs in child process.
> >
> > Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
> > Signed-off-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> > ---
> >  tools/testing/selftests/resctrl/cat_test.c | 30
> ++++++++++++++--------
> >  1 file changed, 20 insertions(+), 10 deletions(-)
> >
> > diff --git a/tools/testing/selftests/resctrl/cat_test.c
> b/tools/testing/selftests/resctrl/cat_test.c
> > index 6a8306b0a109..1f8f5cf94e95 100644
> > --- a/tools/testing/selftests/resctrl/cat_test.c
> > +++ b/tools/testing/selftests/resctrl/cat_test.c
> > @@ -100,10 +100,10 @@ void cat_test_cleanup(void)
> >
> >  int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
> >  {
> > +	struct sigaction sigact;
> >  	unsigned long l_mask, l_mask_1;
> >  	int ret, pipefd[2], sibling_cpu_no;
> >  	char pipe_message;
> > -	pid_t bm_pid;
> >
> >  	cache_size = 0;
> >
> > @@ -181,17 +181,25 @@ int cat_perf_miss_val(int cpu_no, int n, char
> *cache_type)
> >  		strcpy(param.filename, RESULT_FILE_NAME1);
> >  		param.num_of_runs = 0;
> >  		param.cpu_no = sibling_cpu_no;
> > +	} else {
> > +		/*
> > +		 * Register CTRL-C handler for parent, as it has to kill
> > +		 * child process before exiting
> > +		 */
> > +		sigact.sa_sigaction = ctrlc_handler;
> > +		sigemptyset(&sigact.sa_mask);
> > +		sigact.sa_flags = SA_SIGINFO;
> > +		if (sigaction(SIGINT, &sigact, NULL) ||
> > +		    sigaction(SIGTERM, &sigact, NULL) ||
> > +		    sigaction(SIGHUP, &sigact, NULL))
> > +			perror("# sigaction");
> 
> Why keep going at this point?
> 
> I tried this change but I was not able to trigger ctrlc_handler(). It

I tested this change using kselftest framework,
In this case, the timeout command sent a SIGTERM signal,
and then ctrlc_handler() was triggered.
Since the handling of SIGINT and SIGHUP signals is overridden in run_fill_buf(), 
ctrl_handler() may be called if ctrl-c is received.

> seems that the handler is changed soon after (see cat_val()->run_fill_buf())
> and ctrl_handler() (note the subtle name difference) is run instead when
> a SIGINT is received. The value of ctrl_handler() is not clear to me though,
> and it could even be argued that it is broken because it starts with
> free(startptr) and startptr would likely already be free'd at this point
> without resetting its value to NULL.
> 
> From what I understand ctrl_handler() and its installation from
> run_fill_buf() could be removed so that it does not override what is being
> done with this change. Otherwise, from what I can tell, this new handler
> will never run.

I think removing ctrl_handler() is fine. 
In CAT test, it overrides ctrlc_handler().
In other tests(CMT,MBA,MBM), the child process used ctrl_handler() to cleanup itself,
but the parent process cleanup the child process with ctrlc_handler() properly.
Also, avoid using signal().
 fill_buf.c：run_fill_buf()
 201         /* set up ctrl-c handler */
 202         if (signal(SIGINT, ctrl_handler) == SIG_ERR)
 203                 printf("Failed to catch SIGINT!\n");

I removed ctrl_handler() and ran resctrl_tests with and without the kselftest framework.
There is no problem.

Best regards,
Shaopeng Tan