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core: propagate TasksMax= on the root slice to sysctls

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The cgroup "pids" controller is not supported on the root cgroup.
However we expose TasksMax= on it, but currently don't actually apply it
to anything. Let's correct this: if set, let's propagate things to the
right sysctls.

This way we can expose TasksMax= on all units in a somewhat sensible
way.
This commit is contained in:
Lennart Poettering
2018-01-22 16:26:55 +01:00
parent c36a69f4cd
commit 00b5974f70
2 changed files with 40 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/core/cgroup.c
+37 -10
View File
@@ -1028,19 +1028,46 @@ static void cgroup_context_apply(
}
}
if ((apply_mask & CGROUP_MASK_PIDS) && !is_root) {
if (apply_mask & CGROUP_MASK_PIDS) {
if (c->tasks_max != CGROUP_LIMIT_MAX) {
char buf[DECIMAL_STR_MAX(uint64_t) + 2];
if (is_root) {
/* So, the "pids" controller does not expose anything on the root cgroup, in order not to
* replicate knobs exposed elsewhere needlessly. We abstract this away here however, and when
* the knobs of the root cgroup are modified propagate this to the relevant sysctls. There's a
* non-obvious asymmetry however: unlike the cgroup properties we don't really want to take
* exclusive ownership of the sysctls, but we still want to honour things if the user sets
* limits. Hence we employ sort of a one-way strategy: when the user sets a bounded limit
* through us it counts. When the user afterwards unsets it again (i.e. sets it to unbounded)
* it also counts. But if the user never set a limit through us (i.e. we are the default of
* "unbounded") we leave things unmodified. For this we manage a global boolean that we turn on
* the first time we set a limit. Note that this boolean is flushed out on manager reload,
* which is desirable so that there's an offical way to release control of the sysctl from
* systemd: set the limit to unbounded and reload. */
sprintf(buf, "%" PRIu64 "\n", c->tasks_max);
r = cg_set_attribute("pids", path, "pids.max", buf);
} else
r = cg_set_attribute("pids", path, "pids.max", "max");
if (c->tasks_max != CGROUP_LIMIT_MAX) {
u->manager->sysctl_pid_max_changed = true;
r = procfs_tasks_set_limit(c->tasks_max);
} else if (u->manager->sysctl_pid_max_changed)
r = procfs_tasks_set_limit(TASKS_MAX);
else
r = 0;
if (r < 0)
log_unit_full(u, IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
"Failed to set pids.max: %m");
if (r < 0)
log_unit_full(u, IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
"Failed to write to tasks limit sysctls: %m");
} else {
if (c->tasks_max != CGROUP_LIMIT_MAX) {
char buf[DECIMAL_STR_MAX(uint64_t) + 2];
sprintf(buf, "%" PRIu64 "\n", c->tasks_max);
r = cg_set_attribute("pids", path, "pids.max", buf);
} else
r = cg_set_attribute("pids", path, "pids.max", "max");
if (r < 0)
log_unit_full(u, IN_SET(r, -ENOENT, -EROFS, -EACCES) ? LOG_DEBUG : LOG_WARNING, r,
"Failed to set pids.max: %m");
}
}
if (apply_bpf)
src/core/manager.h
+3
View File
@@ -267,6 +267,9 @@ struct Manager {
/* Have we already printed the taint line if necessary? */
bool taint_logged:1;
/* Have we ever changed the "kernel.pid_max" sysctl? */
bool sysctl_pid_max_changed:1;
unsigned test_run_flags:8;
/* If non-zero, exit with the following value when the systemd