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Message-ID: <CAJuCfpEZu9qAm+mWRZRuCFy7yQfpwz0W4N=5Fd1msxWG55yHXg@mail.gmail.com>
Date: Thu, 30 Mar 2023 12:31:22 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Domenico Cerasuolo <cerasuolodomenico@...il.com>
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
brauner@...nel.org, chris@...isdown.name, hannes@...xchg.org
Subject: Re: [PATCH v6 4/4] sched/psi: allow unprivileged polling of N*2s period
On Thu, Mar 30, 2023 at 12:06 PM Domenico Cerasuolo
<cerasuolodomenico@...il.com> wrote:
>
>
>
> On Thu, Mar 30, 2023 at 8:51 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>>
>> On Thu, Mar 30, 2023 at 3:54 AM Domenico Cerasuolo
>> <cerasuolodomenico@...il.com> wrote:
>> >
>> > PSI offers 2 mechanisms to get information about a specific resource
>> > pressure. One is reading from /proc/pressure/<resource>, which gives
>> > average pressures aggregated every 2s. The other is creating a pollable
>> > fd for a specific resource and cgroup.
>> >
>> > The trigger creation requires CAP_SYS_RESOURCE, and gives the
>> > possibility to pick specific time window and threshold, spawing an RT
>> > thread to aggregate the data.
>> >
>> > Systemd would like to provide containers the option to monitor pressure
>> > on their own cgroup and sub-cgroups. For example, if systemd launches a
>> > container that itself then launches services, the container should have
>> > the ability to poll() for pressure in individual services. But neither
>> > the container nor the services are privileged.
>> >
>> > This patch implements a mechanism to allow unprivileged users to create
>> > pressure triggers. The difference with privileged triggers creation is
>> > that unprivileged ones must have a time window that's a multiple of 2s.
>> > This is so that we can avoid unrestricted spawning of rt threads, and
>> > use instead the same aggregation mechanism done for the averages, which
>> > runs independently of any triggers.
>> >
>> > Suggested-by: Johannes Weiner <hannes@...xchg.org>
>> > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
>> > Acked-by: Johannes Weiner <hannes@...xchg.org>
>> > ---
>> > Documentation/accounting/psi.rst | 4 +
>> > include/linux/psi.h | 2 +-
>> > include/linux/psi_types.h | 7 ++
>> > kernel/cgroup/cgroup.c | 2 +-
>> > kernel/sched/psi.c | 175 +++++++++++++++++++------------
>> > 5 files changed, 121 insertions(+), 69 deletions(-)
>> >
>> > diff --git a/Documentation/accounting/psi.rst b/Documentation/accounting/psi.rst
>> > index 5e40b3f437f9..df6062eb3abb 100644
>> > --- a/Documentation/accounting/psi.rst
>> > +++ b/Documentation/accounting/psi.rst
>> > @@ -105,6 +105,10 @@ prevent overly frequent polling. Max limit is chosen as a high enough number
>> > after which monitors are most likely not needed and psi averages can be used
>> > instead.
>> >
>> > +Unprivileged users can also create monitors, with the only limitation that the
>> > +window size must be a multiple of 2s, in order to prevent excessive resource
>> > +usage.
>> > +
>> > When activated, psi monitor stays active for at least the duration of one
>> > tracking window to avoid repeated activations/deactivations when system is
>> > bouncing in and out of the stall state.
>> > diff --git a/include/linux/psi.h b/include/linux/psi.h
>> > index b029a847def1..ab26200c2803 100644
>> > --- a/include/linux/psi.h
>> > +++ b/include/linux/psi.h
>> > @@ -24,7 +24,7 @@ void psi_memstall_leave(unsigned long *flags);
>> >
>> > int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res);
>> > struct psi_trigger *psi_trigger_create(struct psi_group *group,
>> > - char *buf, enum psi_res res);
>> > + char *buf, enum psi_res res, struct file *file);
>> > void psi_trigger_destroy(struct psi_trigger *t);
>> >
>> > __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
>> > diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
>> > index 1819afa8b198..040c089581c6 100644
>> > --- a/include/linux/psi_types.h
>> > +++ b/include/linux/psi_types.h
>> > @@ -151,6 +151,9 @@ struct psi_trigger {
>> >
>> > /* Deferred event(s) from previous ratelimit window */
>> > bool pending_event;
>> > +
>> > + /* Trigger type - PSI_AVGS for unprivileged, PSI_POLL for RT */
>> > + enum psi_aggregators aggregator;
>> > };
>> >
>> > struct psi_group {
>> > @@ -171,6 +174,10 @@ struct psi_group {
>> > /* Aggregator work control */
>> > struct delayed_work avgs_work;
>> >
>> > + /* Unprivileged triggers against N*PSI_FREQ windows */
>> > + struct list_head avg_triggers;
>> > + u32 avg_nr_triggers[NR_PSI_STATES - 1];
>> > +
>> > /* Total stall times and sampled pressure averages */
>> > u64 total[NR_PSI_AGGREGATORS][NR_PSI_STATES - 1];
>> > unsigned long avg[NR_PSI_STATES - 1][3];
>> > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> > index 935e8121b21e..dead36969bba 100644
>> > --- a/kernel/cgroup/cgroup.c
>> > +++ b/kernel/cgroup/cgroup.c
>> > @@ -3761,7 +3761,7 @@ static ssize_t pressure_write(struct kernfs_open_file *of, char *buf,
>> > }
>> >
>> > psi = cgroup_psi(cgrp);
>> > - new = psi_trigger_create(psi, buf, res);
>> > + new = psi_trigger_create(psi, buf, res, of->file);
>> > if (IS_ERR(new)) {
>> > cgroup_put(cgrp);
>> > return PTR_ERR(new);
>> > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
>> > index f3df6a8ff493..e072f6b31bf3 100644
>> > --- a/kernel/sched/psi.c
>> > +++ b/kernel/sched/psi.c
>> > @@ -186,9 +186,14 @@ static void group_init(struct psi_group *group)
>> > seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
>> > group->avg_last_update = sched_clock();
>> > group->avg_next_update = group->avg_last_update + psi_period;
>> > - INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
>> > mutex_init(&group->avgs_lock);
>> > - /* Init trigger-related members */
>> > +
>> > + /* Init avg trigger-related members */
>> > + INIT_LIST_HEAD(&group->avg_triggers);
>> > + memset(group->avg_nr_triggers, 0, sizeof(group->avg_nr_triggers));
>> > + INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
>> > +
>> > + /* Init rtpoll trigger-related members */
>> > atomic_set(&group->rtpoll_scheduled, 0);
>> > mutex_init(&group->rtpoll_trigger_lock);
>> > INIT_LIST_HEAD(&group->rtpoll_triggers);
>> > @@ -430,21 +435,32 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
>> > return growth;
>> > }
>> >
>> > -static u64 update_triggers(struct psi_group *group, u64 now, bool *update_total)
>> > +static u64 update_triggers(struct psi_group *group, u64 now, bool *update_total,
>> > + enum psi_aggregators aggregator)
>> > {
>> > struct psi_trigger *t;
>> > - u64 *total = group->total[PSI_POLL];
>> > + u64 *total = group->total[aggregator];
>> > + struct list_head *triggers;
>> > + u64 *aggregator_total;
>> > *update_total = false;
>> >
>> > + if (aggregator == PSI_AVGS) {
>> > + triggers = &group->avg_triggers;
>> > + aggregator_total = group->avg_total;
>> > + } else {
>> > + triggers = &group->rtpoll_triggers;
>> > + aggregator_total = group->rtpoll_total;
>> > + }
>> > +
>> > /*
>> > * On subsequent updates, calculate growth deltas and let
>> > * watchers know when their specified thresholds are exceeded.
>> > */
>> > - list_for_each_entry(t, &group->rtpoll_triggers, node) {
>> > + list_for_each_entry(t, triggers, node) {
>> > u64 growth;
>> > bool new_stall;
>> >
>> > - new_stall = group->rtpoll_total[t->state] != total[t->state];
>> > + new_stall = aggregator_total[t->state] != total[t->state];
>> >
>> > /* Check for stall activity or a previous threshold breach */
>> > if (!new_stall && !t->pending_event)
>> > @@ -546,6 +562,7 @@ static void psi_avgs_work(struct work_struct *work)
>> > struct delayed_work *dwork;
>> > struct psi_group *group;
>> > u32 changed_states;
>> > + bool update_total;
>> > u64 now;
>> >
>> > dwork = to_delayed_work(work);
>> > @@ -563,8 +580,10 @@ static void psi_avgs_work(struct work_struct *work)
>> > * Once restarted, we'll catch up the running averages in one
>> > * go - see calc_avgs() and missed_periods.
>> > */
>> > - if (now >= group->avg_next_update)
>> > + if (now >= group->avg_next_update) {
>> > + update_triggers(group, now, &update_total, PSI_AVGS);
>> > group->avg_next_update = update_averages(group, now);
>> > + }
>> >
>> > if (changed_states & PSI_STATE_RESCHEDULE) {
>> > schedule_delayed_work(dwork, nsecs_to_jiffies(
>> > @@ -574,7 +593,7 @@ static void psi_avgs_work(struct work_struct *work)
>> > mutex_unlock(&group->avgs_lock);
>> > }
>> >
>> > -static void init_triggers(struct psi_group *group, u64 now)
>> > +static void init_rtpoll_triggers(struct psi_group *group, u64 now)
>> > {
>> > struct psi_trigger *t;
>> >
>> > @@ -667,7 +686,7 @@ static void psi_rtpoll_work(struct psi_group *group)
>> > if (changed_states & group->rtpoll_states) {
>> > /* Initialize trigger windows when entering polling mode */
>> > if (now > group->rtpoll_until)
>> > - init_triggers(group, now);
>> > + init_rtpoll_triggers(group, now);
>> >
>> > /*
>> > * Keep the monitor active for at least the duration of the
>> > @@ -684,7 +703,7 @@ static void psi_rtpoll_work(struct psi_group *group)
>> > }
>> >
>> > if (now >= group->rtpoll_next_update) {
>> > - group->rtpoll_next_update = update_triggers(group, now, &update_total);
>> > + group->rtpoll_next_update = update_triggers(group, now, &update_total, PSI_POLL);
>> > if (update_total)
>> > memcpy(group->rtpoll_total, group->total[PSI_POLL],
>> > sizeof(group->rtpoll_total));
>> > @@ -1254,16 +1273,23 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
>> > }
>> >
>> > struct psi_trigger *psi_trigger_create(struct psi_group *group,
>> > - char *buf, enum psi_res res)
>> > + char *buf, enum psi_res res, struct file *file)
>> > {
>> > struct psi_trigger *t;
>> > enum psi_states state;
>> > u32 threshold_us;
>> > + bool privileged;
>> > u32 window_us;
>> >
>> > if (static_branch_likely(&psi_disabled))
>> > return ERR_PTR(-EOPNOTSUPP);
>> >
>> > + /*
>> > + * Checking the privilege here on file->f_cred implies that a privileged user
>> > + * could open the file and delegate the write to an unprivileged one.
>> > + */
>> > + privileged = cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE);
>> > +
>> > if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
>> > state = PSI_IO_SOME + res * 2;
>> > else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
>> > @@ -1283,6 +1309,13 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
>> > window_us > WINDOW_MAX_US)
>> > return ERR_PTR(-EINVAL);
>> >
>> > + /*
>> > + * Unprivileged users can only use 2s windows so that averages aggregation
>> > + * work is used, and no RT threads need to be spawned.
>> > + */
>> > + if (!privileged && window_us % 2000000)
>> > + return ERR_PTR(-EINVAL);
>> > +
>> > /* Check threshold */
>> > if (threshold_us == 0 || threshold_us > window_us)
>> > return ERR_PTR(-EINVAL);
>> > @@ -1302,31 +1335,40 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
>> > t->last_event_time = 0;
>> > init_waitqueue_head(&t->event_wait);
>> > t->pending_event = false;
>> > + t->aggregator = privileged ? PSI_POLL : PSI_AVGS;
>> >
>> > - mutex_lock(&group->rtpoll_trigger_lock);
>> > + if (privileged) {
>> > + mutex_lock(&group->rtpoll_trigger_lock);
>> >
>> > - if (!rcu_access_pointer(group->rtpoll_task)) {
>> > - struct task_struct *task;
>> > + if (!rcu_access_pointer(group->rtpoll_task)) {
>> > + struct task_struct *task;
>> >
>> > - task = kthread_create(psi_rtpoll_worker, group, "psimon");
>> > - if (IS_ERR(task)) {
>> > - kfree(t);
>> > - mutex_unlock(&group->rtpoll_trigger_lock);
>> > - return ERR_CAST(task);
>> > + task = kthread_create(psi_rtpoll_worker, group, "psimon");
>> > + if (IS_ERR(task)) {
>> > + kfree(t);
>> > + mutex_unlock(&group->rtpoll_trigger_lock);
>> > + return ERR_CAST(task);
>> > + }
>> > + atomic_set(&group->rtpoll_wakeup, 0);
>> > + wake_up_process(task);
>> > + rcu_assign_pointer(group->rtpoll_task, task);
>> > }
>> > - atomic_set(&group->rtpoll_wakeup, 0);
>> > - wake_up_process(task);
>> > - rcu_assign_pointer(group->rtpoll_task, task);
>> > - }
>> >
>> > - list_add(&t->node, &group->rtpoll_triggers);
>> > - group->rtpoll_min_period = min(group->rtpoll_min_period,
>> > - div_u64(t->win.size, UPDATES_PER_WINDOW));
>> > - group->rtpoll_nr_triggers[t->state]++;
>> > - group->rtpoll_states |= (1 << t->state);
>> > + list_add(&t->node, &group->rtpoll_triggers);
>> > + group->rtpoll_min_period = min(group->rtpoll_min_period,
>> > + div_u64(t->win.size, UPDATES_PER_WINDOW));
>> > + group->rtpoll_nr_triggers[t->state]++;
>> > + group->rtpoll_states |= (1 << t->state);
>> >
>> > - mutex_unlock(&group->rtpoll_trigger_lock);
>> > + mutex_unlock(&group->rtpoll_trigger_lock);
>> > + } else {
>> > + mutex_lock(&group->avgs_lock);
>> > +
>> > + list_add(&t->node, &group->avg_triggers);
>> > + group->avg_nr_triggers[t->state]++;
>> >
>> > + mutex_unlock(&group->avgs_lock);
>> > + }
>> > return t;
>> > }
>> >
>> > @@ -1350,34 +1392,41 @@ void psi_trigger_destroy(struct psi_trigger *t)
>> > */
>> > wake_up_pollfree(&t->event_wait);
>> >
>> > - mutex_lock(&group->rtpoll_trigger_lock);
>> > -
>> > - if (!list_empty(&t->node)) {
>> > - struct psi_trigger *tmp;
>> > - u64 period = ULLONG_MAX;
>> > -
>> > - list_del(&t->node);
>> > - group->rtpoll_nr_triggers[t->state]--;
>> > - if (!group->rtpoll_nr_triggers[t->state])
>> > - group->rtpoll_states &= ~(1 << t->state);
>> > - /* reset min update period for the remaining triggers */
>> > - list_for_each_entry(tmp, &group->rtpoll_triggers, node)
>> > - period = min(period, div_u64(tmp->win.size,
>> > - UPDATES_PER_WINDOW));
>> > - group->rtpoll_min_period = period;
>> > - /* Destroy rtpoll_task when the last trigger is destroyed */
>> > - if (group->rtpoll_states == 0) {
>> > - group->rtpoll_until = 0;
>> > - task_to_destroy = rcu_dereference_protected(
>> > - group->rtpoll_task,
>> > - lockdep_is_held(&group->rtpoll_trigger_lock));
>> > - rcu_assign_pointer(group->rtpoll_task, NULL);
>> > - del_timer(&group->rtpoll_timer);
>> > + if (t->aggregator == PSI_AVGS) {
>>
>> Just a nit, in psi_trigger_create() you are handling privileged
>> trigger case first and then unprivileged case. In
>> psi_trigger_destroy() the order is opposite. Would be better to have
>> the same order.
>> In both cases I would prefer:
>>
>> if (t->aggregator == PSI_AVGS) {
>> ...
>> goto out;
>> }
>> // unprivileged case
>> ...
>> out:
>>
>> This would cut down on churn and indents. Not critical from functional
>> point of view, so
>>
>> Acked-by: Suren Baghdasaryan <surenb@...gle.com>
>>
> No problem, I will push v7 with these changes and thanks for the reviews!
>
> Maybe a dumb question but I'm still not familiar with the coding style here,
> `goto out` for destroy is clear. In create though there's just the return statement
> left after the else branch, should I return in the if branch like this:
>
> if (privileged) {
> ...
> return t;
> }
> ...
> return t;
>
> or should the out label just point to the return?
return looks fine to me. Thanks!
>>
>>
>> > + mutex_lock(&group->avgs_lock);
>> > + if (!list_empty(&t->node)) {
>> > + list_del(&t->node);
>> > + group->avg_nr_triggers[t->state]--;
>> > }
>> > + mutex_unlock(&group->avgs_lock);
>> > + } else {
>> > + mutex_lock(&group->rtpoll_trigger_lock);
>> > + if (!list_empty(&t->node)) {
>> > + struct psi_trigger *tmp;
>> > + u64 period = ULLONG_MAX;
>> > +
>> > + list_del(&t->node);
>> > + group->rtpoll_nr_triggers[t->state]--;
>> > + if (!group->rtpoll_nr_triggers[t->state])
>> > + group->rtpoll_states &= ~(1 << t->state);
>> > + /* reset min update period for the remaining triggers */
>> > + list_for_each_entry(tmp, &group->rtpoll_triggers, node)
>> > + period = min(period, div_u64(tmp->win.size,
>> > + UPDATES_PER_WINDOW));
>> > + group->rtpoll_min_period = period;
>> > + /* Destroy rtpoll_task when the last trigger is destroyed */
>> > + if (group->rtpoll_states == 0) {
>> > + group->rtpoll_until = 0;
>> > + task_to_destroy = rcu_dereference_protected(
>> > + group->rtpoll_task,
>> > + lockdep_is_held(&group->rtpoll_trigger_lock));
>> > + rcu_assign_pointer(group->rtpoll_task, NULL);
>> > + del_timer(&group->rtpoll_timer);
>> > + }
>> > + }
>> > + mutex_unlock(&group->rtpoll_trigger_lock);
>> > }
>> >
>> > - mutex_unlock(&group->rtpoll_trigger_lock);
>> > -
>> > /*
>> > * Wait for psi_schedule_rtpoll_work RCU to complete its read-side
>> > * critical section before destroying the trigger and optionally the
>> > @@ -1437,27 +1486,19 @@ static int psi_cpu_show(struct seq_file *m, void *v)
>> > return psi_show(m, &psi_system, PSI_CPU);
>> > }
>> >
>> > -static int psi_open(struct file *file, int (*psi_show)(struct seq_file *, void *))
>> > -{
>> > - if (file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE))
>> > - return -EPERM;
>> > -
>> > - return single_open(file, psi_show, NULL);
>> > -}
>> > -
>> > static int psi_io_open(struct inode *inode, struct file *file)
>> > {
>> > - return psi_open(file, psi_io_show);
>> > + return single_open(file, psi_io_show, NULL);
>> > }
>> >
>> > static int psi_memory_open(struct inode *inode, struct file *file)
>> > {
>> > - return psi_open(file, psi_memory_show);
>> > + return single_open(file, psi_memory_show, NULL);
>> > }
>> >
>> > static int psi_cpu_open(struct inode *inode, struct file *file)
>> > {
>> > - return psi_open(file, psi_cpu_show);
>> > + return single_open(file, psi_cpu_show, NULL);
>> > }
>> >
>> > static ssize_t psi_write(struct file *file, const char __user *user_buf,
>> > @@ -1491,7 +1532,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
>> > return -EBUSY;
>> > }
>> >
>> > - new = psi_trigger_create(&psi_system, buf, res);
>> > + new = psi_trigger_create(&psi_system, buf, res, file);
>> > if (IS_ERR(new)) {
>> > mutex_unlock(&seq->lock);
>> > return PTR_ERR(new);
>> > @@ -1571,7 +1612,7 @@ static int psi_irq_show(struct seq_file *m, void *v)
>> >
>> > static int psi_irq_open(struct inode *inode, struct file *file)
>> > {
>> > - return psi_open(file, psi_irq_show);
>> > + return single_open(file, psi_irq_show, NULL);
>> > }
>> >
>> > static ssize_t psi_irq_write(struct file *file, const char __user *user_buf,
>> > --
>> > 2.34.1
>> >
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