Currently, when pids.max limit is breached in the hierarchy, the event is counted and reported in the cgroup where the forking task resides.

This decouples the limit and the notification caused by the limit making it hard to detect when the actual limit was effected.

Redefine the pids.events:max as: the number of times the limit of the cgroup was hit.

(Implementation differentiates also "forkfail" event but this is currently not exposed as it would better fit into pids.stat. It also differs from pids.events:max only when pids.max is configured on non-leaf cgroups.)

Since it changes semantics of the original "max" event, introduce this change only in the v2 API of the controller and add a cgroup2 mount option to revert to the legacy behavior.

Signed-off-by: Michal Koutný mkoutny@suse.com --- Documentation/admin-guide/cgroup-v1/pids.rst | 3 +- Documentation/admin-guide/cgroup-v2.rst | 13 ++++-- include/linux/cgroup-defs.h | 7 +++- kernel/cgroup/cgroup.c | 15 ++++++- kernel/cgroup/pids.c | 44 +++++++++++++++----- 5 files changed, 64 insertions(+), 18 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/pids.rst b/Documentation/admin-guide/cgroup-v1/pids.rst index 6acebd9e72c8..0f9f9a7b1f6c 100644 --- a/Documentation/admin-guide/cgroup-v1/pids.rst +++ b/Documentation/admin-guide/cgroup-v1/pids.rst @@ -36,7 +36,8 @@ superset of parent/child/pids.current.

The pids.events file contains event counters:

- - max: Number of times fork failed because limit was hit. + - max: Number of times fork failed in the cgroup because limit was hit in + self or ancestors.

Example ------- diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index e73e373297a0..945ff743a3c9 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -239,6 +239,10 @@ cgroup v2 currently supports the following mount options. will not be tracked by the memory controller (even if cgroup v2 is remounted later on).

+ pids_localevents + Represent fork failures inside cgroup's pids.events:max (v1 behavior), + not its limit being hit (v2 behavior). +

Organizing Processes and Threads -------------------------------- @@ -2196,12 +2200,13 @@ PID Interface Files descendants has ever reached.

pids.events - A read-only flat-keyed file which exists on non-root cgroups. The - following entries are defined. Unless specified otherwise, a value - change in this file generates a file modified event. + A read-only flat-keyed file which exists on non-root cgroups. Unless + specified otherwise, a value change in this file generates a file + modified event. The following entries are defined.

max - Number of times fork failed because limit was hit. + The number of times the cgroup's number of processes hit the + limit (see also pids_localevents).

Organisational operations are not blocked by cgroup policies, so it is possible to have pids.current > pids.max. This can be done by either diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index ea48c861cd36..b36690ca0d3f 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -119,7 +119,12 @@ enum { /* * Enable hugetlb accounting for the memory controller. */ - CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING = (1 << 19), + CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING = (1 << 19), + + /* + * Enable legacy local pids.events. + */ + CGRP_ROOT_PIDS_LOCAL_EVENTS = (1 << 20), };

/* cftype->flags */ diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index e32b6972c478..9c9943ea5f89 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1922,6 +1922,7 @@ enum cgroup2_param { Opt_memory_localevents, Opt_memory_recursiveprot, Opt_memory_hugetlb_accounting, + Opt_pids_localevents, nr__cgroup2_params };

@@ -1931,6 +1932,7 @@ static const struct fs_parameter_spec cgroup2_fs_parameters[] = { fsparam_flag("memory_localevents", Opt_memory_localevents), fsparam_flag("memory_recursiveprot", Opt_memory_recursiveprot), fsparam_flag("memory_hugetlb_accounting", Opt_memory_hugetlb_accounting), + fsparam_flag("pids_localevents", Opt_pids_localevents), {} };

@@ -1960,6 +1962,9 @@ static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param case Opt_memory_hugetlb_accounting: ctx->flags |= CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING; return 0; + case Opt_pids_localevents: + ctx->flags |= CGRP_ROOT_PIDS_LOCAL_EVENTS; + return 0; } return -EINVAL; } @@ -1989,6 +1994,11 @@ static void apply_cgroup_root_flags(unsigned int root_flags) cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING; else cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING; + + if (root_flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) + cgrp_dfl_root.flags |= CGRP_ROOT_PIDS_LOCAL_EVENTS; + else + cgrp_dfl_root.flags &= ~CGRP_ROOT_PIDS_LOCAL_EVENTS; } }

@@ -2004,6 +2014,8 @@ static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root seq_puts(seq, ",memory_recursiveprot"); if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING) seq_puts(seq, ",memory_hugetlb_accounting"); + if (cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) + seq_puts(seq, ",pids_localevents"); return 0; }

@@ -7062,7 +7074,8 @@ static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr, "favordynmods\n" "memory_localevents\n" "memory_recursiveprot\n" - "memory_hugetlb_accounting\n"); + "memory_hugetlb_accounting\n" + "pids_localevents\n"); } static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);

diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c index 0e5ec7d59b4d..a557f5c8300b 100644 --- a/kernel/cgroup/pids.c +++ b/kernel/cgroup/pids.c @@ -38,6 +38,14 @@ #define PIDS_MAX (PID_MAX_LIMIT + 1ULL) #define PIDS_MAX_STR "max"

+enum pidcg_event { + /* Fork failed in subtree because this pids_cgroup limit was hit. */ + PIDCG_MAX, + /* Fork failed in this pids_cgroup because ancestor limit was hit. */ + PIDCG_FORKFAIL, + NR_PIDCG_EVENTS, +}; + struct pids_cgroup { struct cgroup_subsys_state css;

@@ -52,8 +60,7 @@ struct pids_cgroup { /* Handle for "pids.events" */ struct cgroup_file events_file;

- /* Number of times fork failed because limit was hit. */ - atomic64_t events_limit; + atomic64_t events[NR_PIDCG_EVENTS]; };

static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css) @@ -148,12 +155,13 @@ static void pids_charge(struct pids_cgroup *pids, int num) * pids_try_charge - hierarchically try to charge the pid count * @pids: the pid cgroup state * @num: the number of pids to charge + * @fail: storage of pid cgroup causing the fail * * This function follows the set limit. It will fail if the charge would cause * the new value to exceed the hierarchical limit. Returns 0 if the charge * succeeded, otherwise -EAGAIN. */ -static int pids_try_charge(struct pids_cgroup *pids, int num) +static int pids_try_charge(struct pids_cgroup *pids, int num, struct pids_cgroup **fail) { struct pids_cgroup *p, *q;

@@ -166,9 +174,10 @@ static int pids_try_charge(struct pids_cgroup *pids, int num) * p->limit is %PIDS_MAX then we know that this test will never * fail. */ - if (new > limit) + if (new > limit) { + *fail = p; goto revert; - + } /* * Not technically accurate if we go over limit somewhere up * the hierarchy, but that's tolerable for the watermark. @@ -236,7 +245,7 @@ static void pids_cancel_attach(struct cgroup_taskset *tset) static int pids_can_fork(struct task_struct *task, struct css_set *cset) { struct cgroup_subsys_state *css; - struct pids_cgroup *pids; + struct pids_cgroup *pids, *pids_over_limit; int err;

if (cset) @@ -244,15 +253,23 @@ static int pids_can_fork(struct task_struct *task, struct css_set *cset) else css = task_css_check(current, pids_cgrp_id, true); pids = css_pids(css); - err = pids_try_charge(pids, 1); + err = pids_try_charge(pids, 1, &pids_over_limit); if (err) { - /* Only log the first time events_limit is incremented. */ - if (atomic64_inc_return(&pids->events_limit) == 1) { + /* compatibility on v1 where events were notified in leaves. */ + if (!cgroup_subsys_on_dfl(pids_cgrp_subsys)) + pids_over_limit = pids; + + /* Only log the first time limit is hit. */ + if (atomic64_inc_return(&pids->events[PIDCG_FORKFAIL]) == 1) { pr_info("cgroup: fork rejected by pids controller in "); - pr_cont_cgroup_path(css->cgroup); + pr_cont_cgroup_path(pids->css.cgroup); pr_cont("\n"); } + atomic64_inc(&pids_over_limit->events[PIDCG_MAX]); + cgroup_file_notify(&pids->events_file); + if (pids_over_limit != pids) + cgroup_file_notify(&pids_over_limit->events_file); } return err; } @@ -340,8 +357,13 @@ static s64 pids_peak_read(struct cgroup_subsys_state *css, static int pids_events_show(struct seq_file *sf, void *v) { struct pids_cgroup *pids = css_pids(seq_css(sf)); + enum pidcg_event pe = PIDCG_MAX; + + if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) || + cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) + pe = PIDCG_FORKFAIL;

- seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events_limit)); + seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events[pe])); return 0; }

Hierarchical counting of events is not practical for watching when a particular pids.max is being hit. Therefore introduce .local flavor of events file (akin to memory controller) that collects only events relevant to given cgroup.

The file is only added to the default hierarchy.

Signed-off-by: Michal Koutný mkoutny@suse.com --- Documentation/admin-guide/cgroup-v2.rst | 5 ++ kernel/cgroup/pids.c | 89 ++++++++++++++++++++----- 2 files changed, 76 insertions(+), 18 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 0b5f77104e8b..782656dcf38b 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2211,6 +2211,11 @@ PID Interface Files The number of times the cgroup's total number of processes hit the pids.max limit (see also pids_localevents).

+ pids.events.local + Similar to pids.events but the fields in the file are local + to the cgroup i.e. not hierarchical. The file modified event + generated on this file reflects only the local events. + Organisational operations are not blocked by cgroup policies, so it is possible to have pids.current > pids.max. This can be done by either setting the limit to be smaller than pids.current, or attaching enough diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c index c09b744d548c..f5cb0ec45b9d 100644 --- a/kernel/cgroup/pids.c +++ b/kernel/cgroup/pids.c @@ -57,10 +57,12 @@ struct pids_cgroup { atomic64_t limit; int64_t watermark;

- /* Handle for "pids.events" */ + /* Handles for pids.events[.local] */ struct cgroup_file events_file; + struct cgroup_file events_local_file;

atomic64_t events[NR_PIDCG_EVENTS]; + atomic64_t events_local[NR_PIDCG_EVENTS]; };

static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css) @@ -244,21 +246,23 @@ static void pids_event(struct pids_cgroup *pids_forking, struct pids_cgroup *p = pids_forking; bool limit = false;

- for (; parent_pids(p); p = parent_pids(p)) { - /* Only log the first time limit is hit. */ - if (atomic64_inc_return(&p->events[PIDCG_FORKFAIL]) == 1) { - pr_info("cgroup: fork rejected by pids controller in "); - pr_cont_cgroup_path(p->css.cgroup); - pr_cont("\n"); - } - cgroup_file_notify(&p->events_file); - - if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) || - cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) - break; + /* Only log the first time limit is hit. */ + if (atomic64_inc_return(&p->events_local[PIDCG_FORKFAIL]) == 1) { + pr_info("cgroup: fork rejected by pids controller in "); + pr_cont_cgroup_path(p->css.cgroup); + pr_cont("\n"); + } + cgroup_file_notify(&p->events_local_file); + if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) || + cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) + return;

- if (p == pids_over_limit) + for (; parent_pids(p); p = parent_pids(p)) { + if (p == pids_over_limit) { limit = true; + atomic64_inc(&p->events_local[PIDCG_MAX]); + cgroup_file_notify(&p->events_local_file); + } if (limit) atomic64_inc(&p->events[PIDCG_MAX]);

@@ -368,20 +372,68 @@ static s64 pids_peak_read(struct cgroup_subsys_state *css, return READ_ONCE(pids->watermark); }

-static int pids_events_show(struct seq_file *sf, void *v) +static int __pids_events_show(struct seq_file *sf, bool local) { struct pids_cgroup *pids = css_pids(seq_css(sf)); enum pidcg_event pe = PIDCG_MAX; + atomic64_t *events;

if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) || - cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) + cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) { pe = PIDCG_FORKFAIL; + local = true; + } + events = local ? pids->events_local : pids->events;

- seq_printf(sf, "max %lld\n", (s64)atomic64_read(&pids->events[pe])); + seq_printf(sf, "max %lld\n", (s64)atomic64_read(&events[pe])); + return 0; +} + +static int pids_events_show(struct seq_file *sf, void *v) +{ + __pids_events_show(sf, false); + return 0; +} + +static int pids_events_local_show(struct seq_file *sf, void *v) +{ + __pids_events_show(sf, true); return 0; }

static struct cftype pids_files[] = { + { + .name = "max", + .write = pids_max_write, + .seq_show = pids_max_show, + .flags = CFTYPE_NOT_ON_ROOT, + }, + { + .name = "current", + .read_s64 = pids_current_read, + .flags = CFTYPE_NOT_ON_ROOT, + }, + { + .name = "peak", + .flags = CFTYPE_NOT_ON_ROOT, + .read_s64 = pids_peak_read, + }, + { + .name = "events", + .seq_show = pids_events_show, + .file_offset = offsetof(struct pids_cgroup, events_file), + .flags = CFTYPE_NOT_ON_ROOT, + }, + { + .name = "events.local", + .seq_show = pids_events_local_show, + .file_offset = offsetof(struct pids_cgroup, events_local_file), + .flags = CFTYPE_NOT_ON_ROOT, + }, + { } /* terminate */ +}; + +static struct cftype pids_files_legacy[] = { { .name = "max", .write = pids_max_write, @@ -407,6 +459,7 @@ static struct cftype pids_files[] = { { } /* terminate */ };

+ struct cgroup_subsys pids_cgrp_subsys = { .css_alloc = pids_css_alloc, .css_free = pids_css_free, @@ -415,7 +468,7 @@ struct cgroup_subsys pids_cgrp_subsys = { .can_fork = pids_can_fork, .cancel_fork = pids_cancel_fork, .release = pids_release, - .legacy_cftypes = pids_files, + .legacy_cftypes = pids_files_legacy, .dfl_cftypes = pids_files, .threaded = true, };

This commit adds (and wires in) new test program for checking basic pids controller functionality -- restricting tasks in a cgroup and correct event counting.

Signed-off-by: Michal Koutný mkoutny@suse.com --- tools/testing/selftests/cgroup/.gitignore | 1 + tools/testing/selftests/cgroup/Makefile | 2 + tools/testing/selftests/cgroup/test_pids.c | 178 +++++++++++++++++++++ 3 files changed, 181 insertions(+) create mode 100644 tools/testing/selftests/cgroup/test_pids.c

diff --git a/tools/testing/selftests/cgroup/.gitignore b/tools/testing/selftests/cgroup/.gitignore index ec635a0ef488..952e4448bf07 100644 --- a/tools/testing/selftests/cgroup/.gitignore +++ b/tools/testing/selftests/cgroup/.gitignore @@ -7,5 +7,6 @@ test_hugetlb_memcg test_kill test_kmem test_memcontrol +test_pids test_zswap wait_inotify diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile index b91f60f3402c..1b897152bab6 100644 --- a/tools/testing/selftests/cgroup/Makefile +++ b/tools/testing/selftests/cgroup/Makefile @@ -15,6 +15,7 @@ TEST_GEN_PROGS += test_hugetlb_memcg TEST_GEN_PROGS += test_kill TEST_GEN_PROGS += test_kmem TEST_GEN_PROGS += test_memcontrol +TEST_GEN_PROGS += test_pids TEST_GEN_PROGS += test_zswap

LOCAL_HDRS += $(selfdir)/clone3/clone3_selftests.h $(selfdir)/pidfd/pidfd.h @@ -29,4 +30,5 @@ $(OUTPUT)/test_hugetlb_memcg: cgroup_util.c $(OUTPUT)/test_kill: cgroup_util.c $(OUTPUT)/test_kmem: cgroup_util.c $(OUTPUT)/test_memcontrol: cgroup_util.c +$(OUTPUT)/test_pids: cgroup_util.c $(OUTPUT)/test_zswap: cgroup_util.c diff --git a/tools/testing/selftests/cgroup/test_pids.c b/tools/testing/selftests/cgroup/test_pids.c new file mode 100644 index 000000000000..9ecb83c6cc5c --- /dev/null +++ b/tools/testing/selftests/cgroup/test_pids.c @@ -0,0 +1,178 @@ +// SPDX-License-Identifier: GPL-2.0 +#define _GNU_SOURCE + +#include <errno.h> +#include <linux/limits.h> +#include <signal.h> +#include <string.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <unistd.h> + +#include "../kselftest.h" +#include "cgroup_util.h" + +static int run_success(const char *cgroup, void *arg) +{ + return 0; +} + +static int run_pause(const char *cgroup, void *arg) +{ + return pause(); +} + +/* + * This test checks that pids.max prevents forking new children above the + * specified limit in the cgroup. + */ +static int test_pids_max(const char *root) +{ + int ret = KSFT_FAIL; + char *cg_pids; + int pid; + + cg_pids = cg_name(root, "pids_test"); + if (!cg_pids) + goto cleanup; + + if (cg_create(cg_pids)) + goto cleanup; + + if (cg_read_strcmp(cg_pids, "pids.max", "max\n")) + goto cleanup; + + if (cg_write(cg_pids, "pids.max", "2")) + goto cleanup; + + if (cg_enter_current(cg_pids)) + goto cleanup; + + pid = cg_run_nowait(cg_pids, run_pause, NULL); + if (pid < 0) + goto cleanup; + + if (cg_run_nowait(cg_pids, run_success, NULL) != -1 || errno != EAGAIN) + goto cleanup; + + if (kill(pid, SIGINT)) + goto cleanup; + + ret = KSFT_PASS; + +cleanup: + cg_enter_current(root); + cg_destroy(cg_pids); + free(cg_pids); + + return ret; +} + +/* + * This test checks that pids.events are counted in cgroup associated with pids.max + */ +static int test_pids_events(const char *root) +{ + int ret = KSFT_FAIL; + char *cg_parent = NULL, *cg_child = NULL; + int pid; + + cg_parent = cg_name(root, "pids_parent"); + cg_child = cg_name(cg_parent, "pids_child"); + if (!cg_parent || !cg_child) + goto cleanup; + + if (cg_create(cg_parent)) + goto cleanup; + if (cg_write(cg_parent, "cgroup.subtree_control", "+pids")) + goto cleanup; + if (cg_create(cg_child)) + goto cleanup; + + if (cg_write(cg_parent, "pids.max", "2")) + goto cleanup; + + if (cg_read_strcmp(cg_child, "pids.max", "max\n")) + goto cleanup; + + if (cg_enter_current(cg_child)) + goto cleanup; + + pid = cg_run_nowait(cg_child, run_pause, NULL); + if (pid < 0) + goto cleanup; + + if (cg_run_nowait(cg_child, run_success, NULL) != -1 || errno != EAGAIN) + goto cleanup; + + if (kill(pid, SIGINT)) + goto cleanup; + + if (cg_read_key_long(cg_child, "pids.events", "max ") != 0) + goto cleanup; + if (cg_read_key_long(cg_parent, "pids.events", "max ") != 1) + goto cleanup; + + + ret = KSFT_PASS; + +cleanup: + cg_enter_current(root); + if (cg_child) + cg_destroy(cg_child); + if (cg_parent) + cg_destroy(cg_parent); + free(cg_child); + free(cg_parent); + + return ret; +} + + + +#define T(x) { x, #x } +struct pids_test { + int (*fn)(const char *root); + const char *name; +} tests[] = { + T(test_pids_max), + T(test_pids_events), +}; +#undef T + +int main(int argc, char **argv) +{ + char root[PATH_MAX]; + + 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"); + + /* + * Check that pids controller is available: + * pids is listed in cgroup.controllers + */ + if (cg_read_strstr(root, "cgroup.controllers", "pids")) + ksft_exit_skip("pids controller isn't available\n"); + + if (cg_read_strstr(root, "cgroup.subtree_control", "pids")) + if (cg_write(root, "cgroup.subtree_control", "+pids")) + ksft_exit_skip("Failed to set pids controller\n"); + + for (int 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\n", tests[i].name); + break; + default: + ksft_test_result_fail("%s\n", tests[i].name); + break; + } + } + + ksft_finished(); +}