[LTP] [PATCH v2 2/2] controllers/memcg_test_3: Add new regression test

[Guangwen Feng]

Hi!

Thanks for your review, and sorry for the late reply.

On 05/30/2017 09:02 PM, Cyril Hrubis wrote:
> Hi!
>> +/*
>> + * This is a regression test for a crash caused by memcg function
>> + * reentrant on RHEL6.  When doing rmdir(), a pending signal can
>> + * interrupt the execution and lead to cgroup_clear_css_refs()
>> + * being entered repeatedly, this results in a BUG_ON().
>> + *
>> + * This bug was introduced by following RHEL6 patch on 2.6.32-488.el6:
>> + *
>> + *  [mm] memcg: fix race condition between memcg teardown and swapin
>> + *  Bugzilla: 1001197
> 
> Can you rather add a link here instead? Just "Bugzilla:" is too vague.
> 

OK, I will add a Bugzilla link instead, and add the patch url of ftp as well.

>> + * This test can crash the buggy kernel on RHEL6.6GA, and the bug
>> + * was fixed by following patch on 2.6.32-536.el6:
>> + *
>> + *  [mm] memcg: fix crash in re-entrant cgroup_clear_css_refs()
>> + *  Bugzilla: 1168185
>> + */
>> +
>> +#include <errno.h>
>> +#include <unistd.h>
>> +#include <stdlib.h>
>> +#include <sys/types.h>
>> +#include <sys/wait.h>
>> +#include "tst_test.h"
>> +
>> +#define MNTPOINT	"memcg"
>> +#define SUBDIR	"memcg/testdir"
>> +
>> +static int mount_flag;
>> +
>> +static struct tst_kern_exv kvers[] = {
>> +	{"RHEL6", "2.6.32-488"},
>> +	{NULL, NULL}
>> +};
>> +
>> +static void sighandler(int sig LTP_ATTRIBUTE_UNUSED)
>> +{
>> +
>> +}
>> +
>> +static void do_child(void)
>> +{
>> +	while (1)
>> +		SAFE_KILL(getppid(), SIGUSR1);
>> +
>> +	exit(0);
>> +}
>> +
>> +static void do_test(void)
>> +{
>> +	int i;
>> +	pid_t cpid = -1;
>> +
>> +	SAFE_SIGNAL(SIGUSR1, sighandler);
>> +
>> +	cpid = SAFE_FORK();
>> +	if (cpid == 0)
>> +		do_child();
> 
> Shouldn't we wait here untill the child is actually running?
> 
> I think that with just 10 iteration in the code below we may as well
> finish the loop too fast.
> 
> So what about incrementing a counter in the signal handler and loop
> until it reaches some small value (50 or something)?
> 

Yes, we need to ensure the synchronization.

It is a good idea to use a counter in signal handler, but 50 or hundreds
is too small, since I tested and found that the signal is triggered way
much faster than the loop in parent.

I have tested that the value can be set to 50000, which makes sure 100%
reproducible in buggy kernel and that the test can be done within 1 second
when there is no bug.

>> +	for (i = 0; i < 10; i++) {
>> +		if (access(SUBDIR, F_OK))
>> +			SAFE_MKDIR(SUBDIR, 0644);
>> +		rmdir(SUBDIR);
>> +	}
>> +
>> +	SAFE_KILL(cpid, SIGKILL);
>> +	SAFE_WAIT(NULL);
>> +
>> +	tst_res(TPASS, "Bug not reproduced");
>> +}
>> +
>> +static void setup(void)
>> +{
>> +	struct utsname buf;
>> +
>> +	SAFE_UNAME(&buf);
>> +	if (!strstr(buf.release, ".el6"))
>> +		tst_brk(TCONF, "This test can only run on RHEL6");
>> +
>> +	if (tst_kvercmp2(2, 6, 24, kvers) < 0)
>> +		tst_brk(TCONF, "This test requires kernel >= 2.6.32-488.el6");
> 
> Why do we skip this test on anything but RHEL6? It does not seem to me
> that the test actually does something that couldn't be tested on any
> other Linux distribution. We only have to check for memcg support here
> instead.
> 

OK, I got it.

Best Regards,
Guangwen Feng

>> +	SAFE_MKDIR(MNTPOINT, 0644);
>> +
>> +	SAFE_MOUNT("memcg", MNTPOINT, "cgroup", 0, "memory");
>> +	mount_flag = 1;
>> +}
>> +
>> +static void cleanup(void)
>> +{
>> +	if (!access(SUBDIR, F_OK))
>> +		SAFE_RMDIR(SUBDIR);
>> +
>> +	if (mount_flag)
>> +		tst_umount(MNTPOINT);
>> +}
>> +
>> +static struct tst_test test = {
>> +	.tid = "memcg_test_3",
>> +	.needs_root = 1,
>> +	.needs_tmpdir = 1,
>> +	.forks_child = 1,
>> +	.setup = setup,
>> +	.cleanup = cleanup,
>> +	.test_all = do_test,
>> +};
>> -- 
>> 1.8.4.2
>>
>>
>>
>>
>> -- 
>> Mailing list info: https://lists.linux.it/listinfo/ltp
>