Re: [LTP] memcontrol03: Bind to single CPU on systems with 64KB pagesize

[linuxtestproject.agent@gmail.com]

Hi Wei,

On Tue Sep 29 02:23:32 2026 +0000, Wei Gao wrote:
> memcontrol03: Bind to single CPU on systems with 64KB pagesize

> diff --git a/testcases/kernel/controllers/memcg/memcontrol03.c b/testcases/kernel/controllers/memcg/memcontrol03.c
> index 96224c4ee..6007d5588 100644
> --- a/testcases/kernel/controllers/memcg/memcontrol03.c
> +++ b/testcases/kernel/controllers/memcg/memcontrol03.c
> @@ -235,6 +235,23 @@ static void test_memcg_min(void)
>  	SAFE_UNLINK(TMPDIR"/tmpfile");
>  }
>  
> +static void setup(void)
> +{

Add #include <sched.h> to memcontrol03.c. The test relies on transitive
inclusion for sched_getcpu(), sched_setaffinity(), and cpu_set_t.

> +	if (getpagesize() >= 64 * 1024) {

Use SAFE_SYSCONF(_SC_PAGESIZE) instead of getpagesize(). The latter is a
legacy API removed in POSIX.1-2001, and memcontrol_common.h already uses
SAFE_SYSCONF(_SC_PAGESIZE).

> +		cpu_set_t mask;
> +		int cpu = sched_getcpu();
> +
> +		if (cpu < 0)
> +			tst_brk(TBROK | TERRNO, "sched_getcpu() failed");
> +
> +		tst_res(TINFO, "Page size >= 64KB, binding to CPU %d", cpu);
> +		CPU_ZERO(&mask);
> +		CPU_SET(cpu, &mask);
> +		if (sched_setaffinity(0, sizeof(mask), &mask))
> +			tst_brk(TBROK | TERRNO, "sched_setaffinity() failed");

On systems with CPU IDs >= 1024 (e.g. large ppc64le systems where
CONFIG_NR_CPUS can be up to 8192), cpu_set_t cannot represent cpu.
CPU_SET() will silently drop the bit, leaving mask empty and causing
sched_setaffinity() to fail with EINVAL. Allocate the mask dynamically
using CPU_ALLOC() or verify cpu < CPU_SETSIZE. Also, check the return
value of sched_setaffinity() with < 0.

Verdict - Needs revision

Pre-existing issues:
- Line 194: sleep(1) is used in a retry loop; use exponential backoff
  polling instead of fixed sleep (Ground Rule 2).
- Lines 166 and 235: string concatenation without spaces (TMPDIR"/tmpfile").

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