Re: [PATCH v3 8/8] selftests/dmabuf-heaps: Add dma-buf memcg accounting tests

Thank you for your contribution! Sashiko AI review found 5 potential issue(s) to consider: - [Medium] selftests/dmabuf-heaps: check_deps() runs before handle_build() in vmtest.sh - [Medium] selftests/dmabuf-heaps: fail instead of skip on EOPNOTSUPP in XFER_CHARGE test - [Medium] selftests/dmabuf-heaps: pidfd_alloc_supported() treats EOPNOTSUPP as supported - [Medium] selftests: dmabuf-heaps: no memory controller check in open_self_cgroupfd() - [Medium] selftests: cgroup: MEMCG_DMABUF_WAIT_RETRIES is shorter than 2s rstat FLUSH_TIME --

commit 764a620a8574ac6b7e6c57e6f71e4c743c373656 Author: Albert Esteve aesteve@redhat.com

selftests/dmabuf-heaps: Add dma-buf memcg accounting tests

This commit adds selftests for dma-buf memcg accounting via charge_fd in DMA_HEAP_IOCTL_ALLOC and DMA_BUF_IOCTL_XFER_CHARGE across the dmabuf-heaps and cgroup test suites, along with a vmtest.sh runner script.

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c index 0ed82347044ed..0b41c3c6f62c1 100644 --- a/tools/testing/selftests/cgroup/test_memcontrol.c +++ b/tools/testing/selftests/cgroup/test_memcontrol.c @@ -19,10 +19,20 @@ #include <errno.h> #include <sys/mman.h> +#include <linux/dma-buf.h> +#include <linux/dma-heap.h> +#include <signal.h> +#include <sys/ioctl.h>

+#include "../pidfd/pidfd.h" #include "kselftest.h" #include "cgroup_util.h" +#define DMA_HEAP_SYSTEM "/dev/dma_heap/system" +#define ONE_MEG (1024 * 1024)

#define MEMCG_SOCKSTAT_WAIT_RETRIES 30 +#define MEMCG_DMABUF_WAIT_RETRIES 15

[Severity: Medium] Is MEMCG_DMABUF_WAIT_RETRIES (15 retries at 100ms intervals, or 1.4 seconds before the final read) long enough to avoid races with the periodic rstat flush in test_memcg_dmabuf() and test_memcg_dmabuf_xfer_at_limit()?

In mm/memcontrol.c, reading memory.stat calls mem_cgroup_flush_stats(), which only flushes rstat synchronously when stats_updates exceeds MEMCG_CHARGE_BATCH * num_online_cpus() (64 * num_online_cpus()):

mm/memcontrol.c:mem_cgroup_flush_stats() if (atomic_long_read(&vmstats->stats_updates) > MEMCG_CHARGE_BATCH * num_online_cpus()) ...

Charging or uncharging a ONE_MEG (1 MB) dma-buf in a fresh child cgroup updates MEMCG_DMABUF by 256 pages on 4KB-page kernels (or 16 pages on 64KB-page kernels). When num_online_cpus() >= 4 (where 256 > 64 * 4 is false) or on >4KB-page kernels, reading memory.stat skips synchronous flushing and relies on the periodic deferred work stats_flush_dwork, which runs every FLUSH_TIME (2UL * HZ, or 2.0 seconds).

In test_memcg_dmabuf(), even if the first poll for ONE_MEG catches a periodic flush, that flush resets stats_updates to 0 and schedules the next stats_flush_dwork 2.0 seconds later. Immediately closing dmabuf_fd adds only 256 to stats_updates, so the subsequent 1.4-second poll for dmabuf == 0 can time out before the next 2.0-second periodic flush runs. Should MEMCG_DMABUF_WAIT_RETRIES be at least 30, matching MEMCG_SOCKSTAT_WAIT_RETRIES?

diff --git a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c index 1d49df6719198..90ef14d2ecba0 100644 --- a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c +++ b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c

[ ... ]

@@ -496,6 +505,218 @@ static void test_alloc_no_fd_leak_on_efault(char *heap_name)

[ ... ]

+/*

• • Probe whether the kernel honours charge_fd in DMA_HEAP_IOCTL_ALLOC.
• */

+static bool pidfd_alloc_supported(int heap_fd) +{

• int devnull_fd, dmabuf_fd = -1, ret;
• devnull_fd = open("/dev/null", O_RDONLY);
• if (devnull_fd < 0)

• return false;
  

• ret = dmabuf_heap_alloc_pidfd(heap_fd, ONE_MEG, 0, devnull_fd, &dmabuf_fd);
• if (dmabuf_fd >= 0) {

• close(dmabuf_fd);
  

• dmabuf_fd = -1;
  

• }
• close(devnull_fd);
• return ret < 0;

+}

[Severity: Medium] What happens in pidfd_alloc_supported() when the kernel is built with CONFIG_MEMCG=n?

In drivers/dma-buf/dma-heap.c, dma_heap_ioctl_allocate() passes a non-zero charge_fd to mem_cgroup_get_from_fd():

drivers/dma-buf/dma-heap.c:dma_heap_ioctl_allocate() if (heap_allocation->charge_fd) { memcg = mem_cgroup_get_from_fd(heap_allocation->charge_fd); if (IS_ERR(memcg)) return ERR_CAST(memcg); }

When CONFIG_MEMCG is disabled, the stub in include/linux/memcontrol.h returns ERR_PTR(-EOPNOTSUPP):

include/linux/memcontrol.h:mem_cgroup_get_from_fd() static inline struct mem_cgroup *mem_cgroup_get_from_fd(int fd) { return ERR_PTR(-EOPNOTSUPP); }

Because dmabuf_heap_alloc_pidfd() returns -1 with errno == EOPNOTSUPP, returning ret < 0 causes pidfd_alloc_supported() to return true when CONFIG_MEMCG=n, and test_alloc_pidfd_self(), test_alloc_pidfd_child(), test_alloc_cgroupfd_self(), and test_xfer_charge_cgroupfd_self() then proceed and report test failures instead of skipping. Should pidfd_alloc_supported() also verify that errno != EOPNOTSUPP (or errno == EINVAL)?

[ ... ]

+static int open_self_cgroupfd(void) +{

• char cgroup_path[PATH_MAX];
• char buf[PATH_MAX];
• FILE *f;
• f = fopen("/proc/self/cgroup", "r");
• if (!f)

• return -1;
  

• cgroup_path[0] = '\0';
• while (fgets(buf, sizeof(buf), f)) {

• char *p = buf;
  

• if (strncmp(p, "0::", 3) == 0) {
  

• 	p += 3;
  

• 	p[strcspn(p, "\n")] = '\0';
  

• 	snprintf(cgroup_path, sizeof(cgroup_path),
  

• 		 "/sys/fs/cgroup%s", p);
  

• 	break;
  

• }
  

• }
• fclose(f);
• if (!cgroup_path[0])

• return -1;
  

• return open(cgroup_path, O_RDONLY | O_DIRECTORY);

+}

+/*

• • Test: allocate charging the calling process's own cgroup via a cgroupfd.
• */

+static void test_alloc_cgroupfd_self(char *heap_name) +{

• int heap_fd = -1, cgroup_fd = -1, dmabuf_fd = -1, ret;
• heap_fd = dmabuf_heap_open(heap_name);
• if (!pidfd_alloc_supported(heap_fd)) {

• ksft_test_result_skip("charge_fd not supported by this kernel\n");
  

• goto out;
  

• }
• cgroup_fd = open_self_cgroupfd();
• if (cgroup_fd < 0) {

• ksft_test_result_skip("cannot open self cgroupfd\n");
  

• goto out;
  

• }
• ret = dmabuf_heap_alloc_pidfd(heap_fd, ONE_MEG, 0, cgroup_fd, &dmabuf_fd);
• ksft_test_result(!ret, "Allocation with cgroupfd %d\n", ret);
• if (dmabuf_fd >= 0)

• close(dmabuf_fd);
  

• close(cgroup_fd);

+out:

• close(heap_fd);

+}

[Severity: Medium] Can test_alloc_cgroupfd_self() and test_xfer_charge_cgroupfd_self() fail with ENOENT instead of skipping when the test binary is run outside vmtest.sh (for example via make run_tests or vmtest.sh -s) in a cgroup where the memory controller is not enabled?

Unlike the pidfd path in mem_cgroup_get_from_fd(), which uses get_mem_cgroup_from_mm() and walks up to an online ancestor, the cgroupfd path requires the memory controller CSS to be directly enabled on the target cgroup itself:

mm/memcontrol.c:mem_cgroup_get_from_fd() cgrp = cgroup_get_from_fd(fd); if (!IS_ERR(cgrp)) { rcu_read_lock(); css = cgroup_css(cgrp, &memory_cgrp_subsys); if (!css || !css_tryget_online(css)) { rcu_read_unlock(); cgroup_put(cgrp); return ERR_PTR(-ENOENT); }

When dmabuf-heap runs in a leaf cgroup (such as a standard systemd user or service scope) whose parent has not enabled +memory in cgroup.subtree_control, or when booted with cgroup_disable=memory, open_self_cgroupfd() still succeeds in opening the directory, and the ioctl fails with ENOENT. Should open_self_cgroupfd() check that memory is active in that cgroup (or should these two tests skip when the ioctl fails with errno == ENOENT)?

+/*

• • Test: transfer a dma-buf's charge to self cgroup via DMA_BUF_IOCTL_XFER_CHARGE.
• */

+static void test_xfer_charge_cgroupfd_self(char *heap_name) +{

• int heap_fd = -1, cgroup_fd = -1, dmabuf_fd = -1, ret;
• struct dma_buf_transfer_charge xfer = { 0 };
• heap_fd = dmabuf_heap_open(heap_name);
• if (!pidfd_alloc_supported(heap_fd)) {

• ksft_test_result_skip("charge_fd not supported by this kernel\n");
  

• goto out;
  

• }
• ret = dmabuf_heap_alloc(heap_fd, ONE_MEG, 0, &dmabuf_fd);
• if (ret) {

• ksft_test_result_fail("Allocation failed %d\n", ret);
  

• goto out;
  

• }
• cgroup_fd = open_self_cgroupfd();
• if (cgroup_fd < 0) {

• ksft_test_result_skip("cannot open self cgroupfd\n");
  

• close(dmabuf_fd);
  

• goto out;
  

• }
• xfer.charge_fd = cgroup_fd;
• ret = ioctl(dmabuf_fd, DMA_BUF_IOCTL_XFER_CHARGE, &xfer);
• ksft_test_result(!ret, "XFER_CHARGE to self cgroupfd %d\n", ret);

[Severity: Medium] Does test_xfer_charge_cgroupfd_self() report a failure instead of skipping when main() iterates over non-system heaps in /dev/dma_heap (such as CMA heaps when CONFIG_DMABUF_HEAPS_CMA=y)?

In drivers/dma-buf/dma-heap.c, dma_heap_ioctl_allocate() validates charge_fd before calling heap->ops->allocate(), so pidfd_alloc_supported() returns true for all heaps. However, in drivers/dma-buf/dma-buf.c, dma_buf_xfer_charge() checks whether the exporter enabled memcg accounting on the buffer:

drivers/dma-buf/dma-buf.c:dma_buf_xfer_charge() if (!dmabuf->memcg_account) return -EOPNOTSUPP;

Because only system_heap sets exp_info.memcg_account = true (while exporters such as cma_heap leave it false), ioctl(dmabuf_fd, DMA_BUF_IOCTL_XFER_CHARGE, &xfer) returns -1 with errno == EOPNOTSUPP on those heaps. Should test_xfer_charge_cgroupfd_self() call ksft_test_result_skip() when ret < 0 and errno == EOPNOTSUPP?

diff --git a/tools/testing/selftests/dmabuf-heaps/vmtest.sh b/tools/testing/selftests/dmabuf-heaps/vmtest.sh new file mode 100755 index 0000000000000..3574b71ca83e8 --- /dev/null +++ b/tools/testing/selftests/dmabuf-heaps/vmtest.sh

[ ... ]

+check_deps() {

• for dep in vng make; do

• if [[ ! -x $(command -v "${dep}") ]]; then
  

• 	echo -e "skip:    dependency ${dep} not found!\n"
  

• 	exit "${KSFT_SKIP}"
  

• fi
  

• done
• if ${SHELL_MODE}; then

• return
  

• fi
• if [[ ! -x "${DMABUF_HEAP_TEST}" ]]; then

• printf "skip:    %s not found!" "${DMABUF_HEAP_TEST}"
  

• printf " Please build the kselftest dmabuf-heaps target (or use -b).\n"
  

• exit "${KSFT_SKIP}"
  

• fi
• if [[ ! -x "${MEMCONTROL_TEST}" ]]; then

• printf "skip:    %s not found!" "${MEMCONTROL_TEST}"
  

• printf " Please build the kselftest cgroup target (or use -b).\n"
  

• exit "${KSFT_SKIP}"
  

• fi

+}

[ ... ]

+trap cleanup EXIT

+check_deps +check_vng +handle_build +make_runner

[Severity: Medium] If vmtest.sh is invoked with -b on a clean tree where the selftest binaries have not been built yet, won't check_deps() exit with KSFT_SKIP before handle_build() has a chance to build them?

In the main flow, check_deps() runs before handle_build(), and inside check_deps() only SHELL_MODE returns early before checking for DMABUF_HEAP_TEST and MEMCONTROL_TEST. Should check_deps() also skip the binary existence checks when BUILD is true (or run after handle_build())?