[PATCH v2 19/23] sched: psi: refactor psi_trigger_create()

Roman Gushchin
2025-10-27T23:22:57Z

Currently psi_trigger_create() does a lot of things:
parses the user text input, allocates and initializes
the psi_trigger structure and turns on the trigger.
It does it slightly different for two existing types
of psi_triggers: system-wide and cgroup-wide.

In order to support a new type of PSI triggers, which
will be owned by a BPF program and won't have a user's
text description, let's refactor psi_trigger_create().

1. Introduce psi_trigger_type enum:
currently PSI_SYSTEM and PSI_CGROUP are valid values.
2. Introduce psi_trigger_params structure to avoid passing
a large number of parameters to psi_trigger_create().
3. Move out the user's input parsing into the new
psi_trigger_parse() helper.
4. Move out the capabilities check into the new
psi_file_privileged() helper.
5. Stop relying on t->of for detecting trigger type.

This commit is a pure refactoring and doesn't bring any
functional changes.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
include/linux/psi.h | 15 +++++--
include/linux/psi_types.h | 33 ++++++++++++++-
kernel/cgroup/cgroup.c | 14 ++++++-
kernel/sched/psi.c | 88 +++++++++++++++++++++++++--------------
4 files changed, 113 insertions(+), 37 deletions(-)

diff --git a/include/linux/psi.h b/include/linux/psi.h
index e0745873e3f2..8178e998d94b 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -23,14 +23,23 @@ void psi_memstall_enter(unsigned long *flags);
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, struct file *file,
- struct kernfs_open_file *of);
+int psi_trigger_parse(struct psi_trigger_params *params, const char *buf);
+struct psi_trigger *psi_trigger_create(struct psi_group *group,
+ const struct psi_trigger_params *param);
void psi_trigger_destroy(struct psi_trigger *t);

__poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
poll_table *wait);

+static inline bool psi_file_privileged(struct file *file)
+{
+ /*
+ * 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.
+ */
+ return cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE);
+}
+
#ifdef CONFIG_CGROUPS
static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
{
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index dd10c22299ab..aa5ed39592cb 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -119,7 +119,38 @@ struct psi_window {
u64 prev_growth;
};

+enum psi_trigger_type {
+ PSI_SYSTEM,
+ PSI_CGROUP,
+};
+
+struct psi_trigger_params {
+ /* Trigger type */
+ enum psi_trigger_type type;
+
+ /* Resource to be monitored */
+ enum psi_res res;
+
+ /* True if all threads should be stalled to trigger */
+ bool full;
+
+ /* Threshold in us */
+ u32 threshold_us;
+
+ /* Window in us */
+ u32 window_us;
+
+ /* Privileged triggers are treated differently */
+ bool privileged;
+
+ /* Link to kernfs open file, only for PSI_CGROUP */
+ struct kernfs_open_file *of;
+};
+
struct psi_trigger {
+ /* Trigger type */
+ enum psi_trigger_type type;
+
/* PSI state being monitored by the trigger */
enum psi_states state;

@@ -135,7 +166,7 @@ struct psi_trigger {
/* Wait queue for polling */
wait_queue_head_t event_wait;

- /* Kernfs file for cgroup triggers */
+ /* Kernfs file for PSI_CGROUP triggers */
struct kernfs_open_file *of;

/* Pending event flag */
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 6ae5f48cf64e..836b28676abc 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4000,6 +4000,12 @@ static ssize_t pressure_write(struct kernfs_open_file *of, char *buf,
struct psi_trigger *new;
struct cgroup *cgrp;
struct psi_group *psi;
+ struct psi_trigger_params params;
+ int err;
+
+ err = psi_trigger_parse(&params, buf);
+ if (err)
+ return err;

cgrp = cgroup_kn_lock_live(of->kn, false);
if (!cgrp)
@@ -4015,7 +4021,13 @@ static ssize_t pressure_write(struct kernfs_open_file *of, char *buf,
}

psi = cgroup_psi(cgrp);
- new = psi_trigger_create(psi, buf, res, of->file, of);
+
+ params.type = PSI_CGROUP;
+ params.res = res;
+ params.privileged = psi_file_privileged(of->file);
+ params.of = of;
+
+ new = psi_trigger_create(psi, &params);
if (IS_ERR(new)) {
cgroup_put(cgrp);
return PTR_ERR(new);
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 59fdb7ebbf22..73fdc79b5602 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -511,7 +511,7 @@ static void update_triggers(struct psi_group *group, u64 now,

/* Generate an event */
if (cmpxchg(&t->event, 0, 1) == 0) {
- if (t->of)
+ if (t->type == PSI_CGROUP)
kernfs_notify(t->of->kn);
else
wake_up_interruptible(&t->event_wait);
@@ -1292,74 +1292,88 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
return 0;
}

-struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
- enum psi_res res, struct file *file,
- struct kernfs_open_file *of)
+int psi_trigger_parse(struct psi_trigger_params *params, const char *buf)
{
- struct psi_trigger *t;
- enum psi_states state;
- u32 threshold_us;
- bool privileged;
- u32 window_us;
+ u32 threshold_us, 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);
+ return -EOPNOTSUPP;

if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
- state = PSI_IO_SOME + res * 2;
+ params->full = false;
else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
- state = PSI_IO_FULL + res * 2;
+ params->full = true;
else
- return ERR_PTR(-EINVAL);
+ return -EINVAL;
+
+ params->threshold_us = threshold_us;
+ params->window_us = window_us;
+ return 0;
+}
+
+struct psi_trigger *psi_trigger_create(struct psi_group *group,
+ const struct psi_trigger_params *params)
+{
+ struct psi_trigger *t;
+ enum psi_states state;
+
+ if (static_branch_likely(&psi_disabled))
+ return ERR_PTR(-EOPNOTSUPP);
+
+ state = params->full ? PSI_IO_FULL : PSI_IO_SOME;
+ state += params->res * 2;

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
- if (res == PSI_IRQ && --state != PSI_IRQ_FULL)
+ if (params->res == PSI_IRQ && --state != PSI_IRQ_FULL)
return ERR_PTR(-EINVAL);
#endif

if (state >= PSI_NONIDLE)
return ERR_PTR(-EINVAL);

- if (window_us == 0 || window_us > WINDOW_MAX_US)
+ if (params->window_us == 0 || params->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)
+ if (!params->privileged && params->window_us % 2000000)
return ERR_PTR(-EINVAL);

/* Check threshold */
- if (threshold_us == 0 || threshold_us > window_us)
+ if (params->threshold_us == 0 || params->threshold_us > params->window_us)
return ERR_PTR(-EINVAL);

t = kmalloc(sizeof(*t), GFP_KERNEL);
if (!t)
return ERR_PTR(-ENOMEM);

+ t->type = params->type;
t->group = group;
t->state = state;
- t->threshold = threshold_us * NSEC_PER_USEC;
- t->win.size = window_us * NSEC_PER_USEC;
+ t->threshold = params->threshold_us * NSEC_PER_USEC;
+ t->win.size = params->window_us * NSEC_PER_USEC;
window_reset(&t->win, sched_clock(),
group->total[PSI_POLL][t->state], 0);

t->event = 0;
t->last_event_time = 0;
- t->of = of;
- if (!of)
+
+ switch (params->type) {
+ case PSI_SYSTEM:
init_waitqueue_head(&t->event_wait);
+ t->of = NULL;
+ break;
+ case PSI_CGROUP:
+ t->of = params->of;
+ break;
+ }
+
t->pending_event = false;
- t->aggregator = privileged ? PSI_POLL : PSI_AVGS;
+ t->aggregator = params->privileged ? PSI_POLL : PSI_AVGS;

- if (privileged) {
+ if (params->privileged) {
mutex_lock(&group->rtpoll_trigger_lock);

if (!rcu_access_pointer(group->rtpoll_task)) {
@@ -1412,7 +1426,7 @@ void psi_trigger_destroy(struct psi_trigger *t)
* being accessed later. Can happen if cgroup is deleted from under a
* polling process.
*/
- if (t->of)
+ if (t->type == PSI_CGROUP)
kernfs_notify(t->of->kn);
else
wake_up_interruptible(&t->event_wait);
@@ -1492,7 +1506,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr,
if (!t)
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;

- if (t->of)
+ if (t->type == PSI_CGROUP)
kernfs_generic_poll(t->of, wait);
else
poll_wait(file, &t->event_wait, wait);
@@ -1541,6 +1555,8 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
size_t buf_size;
struct seq_file *seq;
struct psi_trigger *new;
+ struct psi_trigger_params params;
+ int err;

if (static_branch_likely(&psi_disabled))
return -EOPNOTSUPP;
@@ -1554,6 +1570,10 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,

buf[buf_size - 1] = '\0';

+ err = psi_trigger_parse(&params, buf);
+ if (err)
+ return err;
+
seq = file->private_data;

/* Take seq->lock to protect seq->private from concurrent writes */
@@ -1565,7 +1585,11 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
return -EBUSY;
}

- new = psi_trigger_create(&psi_system, buf, res, file, NULL);
+ params.type = PSI_SYSTEM;
+ params.res = res;
+ params.privileged = psi_file_privileged(file);
+
+ new = psi_trigger_create(&psi_system, &params);
if (IS_ERR(new)) {
mutex_unlock(&seq->lock);
return PTR_ERR(new);
--
2.51.0