On Fri, Mar 27, 2026 at 9:53 AM Albert Esteve <[email protected]> wrote:
>
> Currently, tools/testing/selftests/cgroup/ does not include
> a dmem-specific test binary. This leaves dmem charge and
> limit behavior largely unvalidated in kselftest coverage.
>
> Add test_dmem and wire it into the cgroup selftests Makefile.
> The new test exercises dmem controller behavior through the
> dmem_selftest debugfs interface for the dmem_selftest region.
>
> The test adds three complementary checks:
> - test_dmem_max creates a nested hierarchy with per-leaf
> dmem.max values and verifies that over-limit charges
> fail while in-limit charges succeed with bounded rounding
> in dmem.current.
> - test_dmem_min and test_dmem_low verify that charging
> from a cgroup with the corresponding protection knob
> set updates dmem.current as expected.
> - test_dmem_charge_byte_granularity validates accounting
> bounds for non-page-aligned charge sizes and
> uncharge-to-zero behavior.
>
> This provides deterministic userspace coverage for dmem
> accounting and hard-limit enforcement using a test helper
> module, without requiring subsystem-specific production
> drivers.
>
> Signed-off-by: Albert Esteve <[email protected]>
> ---
> tools/testing/selftests/cgroup/.gitignore | 1 +
> tools/testing/selftests/cgroup/Makefile | 2 +
> tools/testing/selftests/cgroup/test_dmem.c | 487
> +++++++++++++++++++++++++++++
> 3 files changed, 490 insertions(+)
>
> diff --git a/tools/testing/selftests/cgroup/.gitignore
> b/tools/testing/selftests/cgroup/.gitignore
> index 952e4448bf070..ea2322598217d 100644
> --- a/tools/testing/selftests/cgroup/.gitignore
> +++ b/tools/testing/selftests/cgroup/.gitignore
> @@ -2,6 +2,7 @@
> test_core
> test_cpu
> test_cpuset
> +test_dmem
> test_freezer
> test_hugetlb_memcg
> test_kill
> diff --git a/tools/testing/selftests/cgroup/Makefile
> b/tools/testing/selftests/cgroup/Makefile
> index e01584c2189ac..e1a5e9316620e 100644
> --- a/tools/testing/selftests/cgroup/Makefile
> +++ b/tools/testing/selftests/cgroup/Makefile
> @@ -10,6 +10,7 @@ TEST_GEN_FILES := wait_inotify
> TEST_GEN_PROGS = test_core
> TEST_GEN_PROGS += test_cpu
> TEST_GEN_PROGS += test_cpuset
> +TEST_GEN_PROGS += test_dmem
> TEST_GEN_PROGS += test_freezer
> TEST_GEN_PROGS += test_hugetlb_memcg
> TEST_GEN_PROGS += test_kill
> @@ -26,6 +27,7 @@ include lib/libcgroup.mk
> $(OUTPUT)/test_core: $(LIBCGROUP_O)
> $(OUTPUT)/test_cpu: $(LIBCGROUP_O)
> $(OUTPUT)/test_cpuset: $(LIBCGROUP_O)
> +$(OUTPUT)/test_dmem: $(LIBCGROUP_O)
> $(OUTPUT)/test_freezer: $(LIBCGROUP_O)
> $(OUTPUT)/test_hugetlb_memcg: $(LIBCGROUP_O)
> $(OUTPUT)/test_kill: $(LIBCGROUP_O)
> diff --git a/tools/testing/selftests/cgroup/test_dmem.c
> b/tools/testing/selftests/cgroup/test_dmem.c
> new file mode 100644
> index 0000000000000..cdd5cb7206f16
> --- /dev/null
> +++ b/tools/testing/selftests/cgroup/test_dmem.c
> @@ -0,0 +1,487 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Test the dmem (device memory) cgroup controller.
> + *
> + * Depends on dmem_selftest kernel module.
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <linux/limits.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +#include "kselftest.h"
> +#include "cgroup_util.h"
> +
> +/* kernel/cgroup/dmem_selftest.c */
> +#define DM_SELFTEST_REGION "dmem_selftest"
> +#define DM_SELFTEST_CHARGE "/sys/kernel/debug/dmem_selftest/charge"
> +#define DM_SELFTEST_UNCHARGE "/sys/kernel/debug/dmem_selftest/uncharge"
> +
> +/*
> + * Parse the first line of dmem.capacity (root):
> + * "<name> <size_in_bytes>"
> + * Returns 1 if a region was found, 0 if capacity is empty, -1 on read error.
> + */
> +static int parse_first_region(const char *root, char *name, size_t name_len,
> + unsigned long long *size_out)
> +{
> + char buf[4096];
> + char nm[256];
> + unsigned long long sz;
> +
> + if (cg_read(root, "dmem.capacity", buf, sizeof(buf)) < 0)
> + return -1;
> +
> + if (sscanf(buf, "%255s %llu", nm, &sz) < 2)
> + return 0;
> +
> + if (name_len <= strlen(nm))
> + return -1;
> +
> + strcpy(name, nm);
> + *size_out = sz;
> + return 1;
> +}
> +
> +/*
> + * Read the numeric limit for @region_name from a multiline
> + * dmem.{min,low,max} file. Returns bytes,
> + * or -1 if the line is "<name> max", or -2 if missing/err.
> + */
> +static long long dmem_read_limit_for_region(const char *cgroup, const char
> *ctrl,
> + const char *region_name)
> +{
> + char buf[4096];
> + char *line, *saveptr = NULL;
> + char fname[256];
> + char fval[64];
> +
> + if (cg_read(cgroup, ctrl, buf, sizeof(buf)) < 0)
> + return -2;
> +
> + for (line = strtok_r(buf, "\n", &saveptr); line;
> + line = strtok_r(NULL, "\n", &saveptr)) {
> + if (!line[0])
> + continue;
> + if (sscanf(line, "%255s %63s", fname, fval) != 2)
> + continue;
> + if (strcmp(fname, region_name))
> + continue;
> + if (!strcmp(fval, "max"))
> + return -1;
> + return strtoll(fval, NULL, 0);
> + }
> + return -2;
> +}
> +
> +static long long dmem_read_limit(const char *cgroup, const char *ctrl)
> +{
> + return dmem_read_limit_for_region(cgroup, ctrl, DM_SELFTEST_REGION);
> +}
> +
> +static int dmem_write_limit(const char *cgroup, const char *ctrl,
> + const char *val)
> +{
> + char wr[512];
> +
> + snprintf(wr, sizeof(wr), "%s %s", DM_SELFTEST_REGION, val);
> + return cg_write(cgroup, ctrl, wr);
> +}
> +
> +static int dmem_selftest_charge_bytes(unsigned long long bytes)
> +{
> + char wr[32];
> +
> + snprintf(wr, sizeof(wr), "%llu", bytes);
> + return write_text(DM_SELFTEST_CHARGE, wr, strlen(wr));
> +}
> +
> +static int dmem_selftest_uncharge(void)
> +{
> + return write_text(DM_SELFTEST_UNCHARGE, "\n", 1);
> +}
> +
> +/*
> + * First, this test creates the following hierarchy:
> + * A
> + * A/B dmem.max=1M
> + * A/B/C dmem.max=75K
> + * A/B/D dmem.max=25K
> + * A/B/E dmem.max=8K
> + * A/B/F dmem.max=0
> + *
> + * Then for each leaf cgroup it tries to charge above dmem.max
> + * and expects the charge request to fail and dmem.current to
> + * remain unchanged.
> + *
> + * For leaves with non-zero dmem.max, it additionally charges a
> + * smaller amount and verifies accounting grows within one PAGE_SIZE
> + * rounding bound, then uncharges and verifies dmem.current returns
> + * to the previous value.
> + *
> + */
> +static int test_dmem_max(const char *root)
> +{
> + static const char * const leaf_max[] = { "75K", "25K", "8K", "0" };
> + static const unsigned long long fail_sz[] = {
> + (75ULL * 1024ULL) + 1ULL,
> + (25ULL * 1024ULL) + 1ULL,
> + (8ULL * 1024ULL) + 1ULL,
> + 1ULL
> + };
> + static const unsigned long long pass_sz[] = {
> + 4096ULL, 4096ULL, 4096ULL, 0ULL
> + };
> + char *parent[2] = {NULL};
> + char *children[4] = {NULL};
> + unsigned long long cap;
> + char region[256];
> + long long page_size;
> + long long cur_before, cur_after;
> + int ret = KSFT_FAIL;
> + int charged = 0;
> + int in_child = 0;
> + long long v;
> + int i;
> +
> + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> + return KSFT_SKIP;
> +
> + if (parse_first_region(root, region, sizeof(region), &cap) != 1)
> + return KSFT_SKIP;
> + if (strcmp(region, DM_SELFTEST_REGION) != 0)
> + return KSFT_SKIP;
> +
> + page_size = sysconf(_SC_PAGESIZE);
> + if (page_size <= 0)
> + goto cleanup;
> +
> + parent[0] = cg_name(root, "dmem_prot_0");
> + parent[1] = cg_name(parent[0], "dmem_prot_1");
> + if (!parent[0] || !parent[1])
> + goto cleanup;
> +
> + if (cg_create(parent[0]))
> + goto cleanup;
> +
> + if (cg_write(parent[0], "cgroup.subtree_control", "+dmem"))
> + goto cleanup;
> +
> + if (cg_create(parent[1]))
> + goto cleanup;
> +
> + if (cg_write(parent[1], "cgroup.subtree_control", "+dmem"))
> + goto cleanup;
> +
> + for (i = 0; i < 4; i++) {
> + children[i] = cg_name_indexed(parent[1], "dmem_child", i);
> + if (!children[i])
> + goto cleanup;
> + if (cg_create(children[i]))
> + goto cleanup;
> + }
> +
> + if (dmem_write_limit(parent[1], "dmem.max", "1M"))
> + goto cleanup;
> + for (i = 0; i < 4; i++)
> + if (dmem_write_limit(children[i], "dmem.max", leaf_max[i]))
> + goto cleanup;
> +
> + v = dmem_read_limit(parent[1], "dmem.max");
> + if (!values_close(v, 1024LL * 1024LL, 3))
> + goto cleanup;
> + v = dmem_read_limit(children[0], "dmem.max");
> + if (!values_close(v, 75LL * 1024LL, 3))
> + goto cleanup;
> + v = dmem_read_limit(children[1], "dmem.max");
> + if (!values_close(v, 25LL * 1024LL, 3))
> + goto cleanup;
> + v = dmem_read_limit(children[2], "dmem.max");
> + if (!values_close(v, 8LL * 1024LL, 3))
> + goto cleanup;
> + v = dmem_read_limit(children[3], "dmem.max");
> + if (v != 0)
> + goto cleanup;
> +
> + for (i = 0; i < 4; i++) {
> + if (cg_enter_current(children[i]))
> + goto cleanup;
> + in_child = 1;
> +
> + cur_before = dmem_read_limit(children[i], "dmem.current");
> + if (cur_before < 0)
> + goto cleanup;
> +
> + if (dmem_selftest_charge_bytes(fail_sz[i]) == 0)
This should be '>= 0', dmem_selftest_charge_bytes() returns the
written bytes on success.
I will fix it in the next iteration.
> + goto cleanup;
> +
> + cur_after = dmem_read_limit(children[i], "dmem.current");
> + if (cur_after != cur_before)
> + goto cleanup;
> +
> + if (pass_sz[i] > 0) {
> + if (dmem_selftest_charge_bytes(pass_sz[i]) < 0)
> + goto cleanup;
> + charged = 1;
> +
> + cur_after = dmem_read_limit(children[i],
> "dmem.current");
> + if (cur_after < cur_before + (long long)pass_sz[i])
> + goto cleanup;
> + if (cur_after > cur_before + (long long)pass_sz[i] +
> page_size)
> + goto cleanup;
> +
> + if (dmem_selftest_uncharge() < 0)
> + goto cleanup;
> + charged = 0;
> +
> + cur_after = dmem_read_limit(children[i],
> "dmem.current");
> + if (cur_after != cur_before)
> + goto cleanup;
> + }
> +
> + if (cg_enter_current(root))
> + goto cleanup;
> + in_child = 0;
> + }
> +
> + ret = KSFT_PASS;
> +
> +cleanup:
> + if (charged)
> + dmem_selftest_uncharge();
> + if (in_child)
> + cg_enter_current(root);
> + for (i = 3; i >= 0; i--) {
> + if (!children[i])
> + continue;
> + cg_destroy(children[i]);
> + free(children[i]);
> + }
> + for (i = 1; i >= 0; i--) {
> + if (!parent[i])
> + continue;
> + cg_destroy(parent[i]);
> + free(parent[i]);
> + }
> + return ret;
> +}
> +
> +/*
> + * This test sets dmem.min and dmem.low on a child cgroup, then charge
> + * from that context and verify dmem.current tracks the charged bytes
> + * (within one page rounding).
> + */
> +static int test_dmem_charge_with_attr(const char *root, bool min)
> +{
> + char region[256];
> + unsigned long long cap;
> + const unsigned long long charge_sz = 12345ULL;
> + const char *attribute = min ? "dmem.min" : "dmem.low";
> + int ret = KSFT_FAIL;
> + char *cg = NULL;
> + long long cur;
> + long long page_size;
> + int charged = 0;
> + int in_child = 0;
> +
> + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> + return KSFT_SKIP;
> +
> + if (parse_first_region(root, region, sizeof(region), &cap) != 1)
> + return KSFT_SKIP;
> + if (strcmp(region, DM_SELFTEST_REGION) != 0)
> + return KSFT_SKIP;
> +
> + page_size = sysconf(_SC_PAGESIZE);
> + if (page_size <= 0)
> + goto cleanup;
> +
> + cg = cg_name(root, "test_dmem_attr");
> + if (!cg)
> + goto cleanup;
> +
> + if (cg_create(cg))
> + goto cleanup;
> +
> + if (cg_enter_current(cg))
> + goto cleanup;
> + in_child = 1;
> +
> + if (dmem_write_limit(cg, attribute, "16K"))
> + goto cleanup;
> +
> + if (dmem_selftest_charge_bytes(charge_sz) < 0)
> + goto cleanup;
> + charged = 1;
> +
> + cur = dmem_read_limit(cg, "dmem.current");
> + if (cur < (long long)charge_sz)
> + goto cleanup;
> + if (cur > (long long)charge_sz + page_size)
> + goto cleanup;
> +
> + if (dmem_selftest_uncharge() < 0)
> + goto cleanup;
> + charged = 0;
> +
> + cur = dmem_read_limit(cg, "dmem.current");
> + if (cur != 0)
> + goto cleanup;
> +
> + ret = KSFT_PASS;
> +
> +cleanup:
> + if (charged)
> + dmem_selftest_uncharge();
> + if (in_child)
> + cg_enter_current(root);
> + cg_destroy(cg);
> + free(cg);
> + return ret;
> +}
> +
> +static int test_dmem_min(const char *root)
> +{
> + return test_dmem_charge_with_attr(root, "dmem.min");
> +}
> +
> +static int test_dmem_low(const char *root)
> +{
> + return test_dmem_charge_with_attr(root, "dmem.low");
> +}
> +
> +/*
> + * This test charges non-page-aligned byte sizes and verify dmem.current
> + * stays consistent: it must account at least the requested bytes and
> + * never exceed one kernel page of rounding overhead. Then uncharge must
> + * return usage to 0.
> + */
> +static int test_dmem_charge_byte_granularity(const char *root)
> +{
> + static const unsigned long long sizes[] = { 1ULL, 4095ULL, 4097ULL,
> 12345ULL };
> + char *cg = NULL;
> + unsigned long long cap;
> + char region[256];
> + long long cur;
> + long long page_size;
> + int ret = KSFT_FAIL;
> + int charged = 0;
> + int in_child = 0;
> + size_t i;
> +
> + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> + return KSFT_SKIP;
> +
> + if (parse_first_region(root, region, sizeof(region), &cap) != 1)
> + return KSFT_SKIP;
> + if (strcmp(region, DM_SELFTEST_REGION) != 0)
> + return KSFT_SKIP;
> +
> + page_size = sysconf(_SC_PAGESIZE);
> + if (page_size <= 0)
> + goto cleanup;
> +
> + cg = cg_name(root, "dmem_dbg_byte_gran");
> + if (!cg)
> + goto cleanup;
> +
> + if (cg_create(cg))
> + goto cleanup;
> +
> + if (dmem_write_limit(cg, "dmem.max", "8M"))
> + goto cleanup;
> +
> + if (cg_enter_current(cg))
> + goto cleanup;
> + in_child = 1;
> +
> + for (i = 0; i < ARRAY_SIZE(sizes); i++) {
> + if (dmem_selftest_charge_bytes(sizes[i]) < 0)
> + goto cleanup;
> + charged = 1;
> +
> + cur = dmem_read_limit(cg, "dmem.current");
> + if (cur < (long long)sizes[i])
> + goto cleanup;
> + if (cur > (long long)sizes[i] + page_size)
> + goto cleanup;
> +
> + if (dmem_selftest_uncharge() < 0)
> + goto cleanup;
> + charged = 0;
> +
> + cur = dmem_read_limit(cg, "dmem.current");
> + if (cur != 0)
> + goto cleanup;
> + }
> +
> + ret = KSFT_PASS;
> +
> +cleanup:
> + if (charged)
> + dmem_selftest_uncharge();
> + if (in_child)
> + cg_enter_current(root);
> + if (cg) {
> + cg_destroy(cg);
> + free(cg);
> + }
> + return ret;
> +}
> +
> +#define T(x) { x, #x }
> +struct dmem_test {
> + int (*fn)(const char *root);
> + const char *name;
> +} tests[] = {
> + T(test_dmem_max),
> + T(test_dmem_min),
> + T(test_dmem_low),
> + T(test_dmem_charge_byte_granularity),
> +};
> +#undef T
> +
> +int main(int argc, char **argv)
> +{
> + char root[PATH_MAX];
> + int i;
> +
> + ksft_print_header();
> + ksft_set_plan(ARRAY_SIZE(tests));
> +
> + if (cg_find_unified_root(root, sizeof(root), NULL))
> + ksft_exit_skip("cgroup v2 isn't mounted\n");
> +
> + if (cg_read_strstr(root, "cgroup.controllers", "dmem"))
> + ksft_exit_skip("dmem controller isn't available
> (CONFIG_CGROUP_DMEM?)\n");
> +
> + if (cg_read_strstr(root, "cgroup.subtree_control", "dmem"))
> + if (cg_write(root, "cgroup.subtree_control", "+dmem"))
> + ksft_exit_skip("Failed to enable dmem controller\n");
> +
> + for (i = 0; i < ARRAY_SIZE(tests); i++) {
> + switch (tests[i].fn(root)) {
> + case KSFT_PASS:
> + ksft_test_result_pass("%s\n", tests[i].name);
> + break;
> + case KSFT_SKIP:
> + ksft_test_result_skip(
> + "%s (need CONFIG_DMEM_SELFTEST, modprobe
> dmem_selftest)\n",
> + tests[i].name);
> + break;
> + default:
> + ksft_test_result_fail("%s\n", tests[i].name);
> + break;
> + }
> + }
> +
> + ksft_finished();
> +}
>
> --
> 2.52.0
>
