[LTP] [PATCH v2] lib: Do not fail a test if oom score cannot be adjusted.

[xuyang2018.jy@fujitsu.com]

Hi Petr, All
> Hi Cyril, all,
>
>> From: Petr Vorel<pvorel@suse.cz>
>
>> Setting value<  0 in /proc/*/oom_score_adj requires CAP_SYS_RESOURCE or
>> CAP_SYS_ADMIN.
Here will mislead user.
Since the default oom_score_adj value is 0, so we can not set a value < 0.

The value of /proc/<pid>/oom_score_adj may be reduced no lower than the 
last value set by a CAP_SYS_RESOURCE process. To reduce the value any 
lower requires CAP_SYS_RESOURCE.

Also looks man 7 capabilities, CAP_SYS_ADMIN doesn't have this cap and I 
have do a test to verify this

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include "tst_test.h"
#include "tst_capability.h"

static void run(void)
{
         FILE *f;

         f = fopen("/proc/self/oom_score_adj", "w");
         if (!f)
                 tst_res(TFAIL, "non-exist");

         if (fprintf(f, "%d", -200) <= 0)
                 tst_res(TFAIL, "write failed");

         if (fclose(f))
                 tst_res(TFAIL, "close %d",errno);

         tst_res(TPASS, "write pass");
}

static struct tst_test test = {
         .test_all = run,
         .caps = (struct tst_cap []) {
                 TST_CAP(TST_CAP_REQ, CAP_SYS_ADMIN),
                 TST_CAP(TST_CAP_DROP, CAP_SYS_RESOURCE),
                 {}
         },
};

It still fails if we only have CAP_SYS_ADMIN.

Best Regards
Yang Xu

  However setting the library process score is a best
>> effort operation, so let's skip it silently when the user is not
>> privileged to do so.
> +1
>
> LGTM, thanks for this version, I'm for merging it.
>
> Also tested locally and on CI, working as expected.
> https://github.com/pevik/ltp/runs/4607602484?check_suite_focus=true
>
> Kind regards,
> Petr