[PATCH v3 2/9] cgroup/cpuset: Extract out CS_CPU_EXCLUSIVE & CS_SCHED_LOAD_BALANCE handling

Waiman Long
2023-06-27T00:55:22Z

Extract out the setting of CS_CPU_EXCLUSIVE and CS_SCHED_LOAD_BALANCE
flags as well as the rebuilding of scheduling domains into the new
update_partition_exclusive() and update_partition_sd_lb() helper
functions to simplify the logic. The update_partition_exclusive()
helper is called mainly at the beginning of the caller, but it may be
called at the end too. The update_partition_sd_lb() helper is called
at the end of the caller.

This patch should reduce the chance that cpuset partition will end up
in an incorrect state.

Signed-off-by: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
kernel/cgroup/cpuset.c | 141 +++++++++++++++++++++++++----------------
1 file changed, 86 insertions(+), 55 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 170e342b07e3..ade33e50ffe2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1255,7 +1255,7 @@ static void update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
static void compute_effective_cpumask(struct cpumask *new_cpus,
struct cpuset *cs, struct cpuset *parent)
{
- if (parent->nr_subparts_cpus) {
+ if (parent->nr_subparts_cpus && is_partition_valid(cs)) {
cpumask_or(new_cpus, parent->effective_cpus,
parent->subparts_cpus);
cpumask_and(new_cpus, new_cpus, cs->cpus_allowed);
@@ -1277,6 +1277,50 @@ enum subparts_cmd {

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
int turning_on);
+
+/*
+ * Update partition exclusive flag
+ *
+ * Return: 0 if successful, an error code otherwise
+ */
+static int update_partition_exclusive(struct cpuset *cs, int new_prs)
+{
+ bool exclusive = (new_prs > 0);
+
+ if (exclusive && !is_cpu_exclusive(cs)) {
+ if (update_flag(CS_CPU_EXCLUSIVE, cs, 1))
+ return PERR_NOTEXCL;
+ } else if (!exclusive && is_cpu_exclusive(cs)) {
+ /* Turning off CS_CPU_EXCLUSIVE will not return error */
+ update_flag(CS_CPU_EXCLUSIVE, cs, 0);
+ }
+ return 0;
+}
+
+/*
+ * Update partition load balance flag and/or rebuild sched domain
+ *
+ * Changing load balance flag will automatically call
+ * rebuild_sched_domains_locked().
+ */
+static void update_partition_sd_lb(struct cpuset *cs, int old_prs)
+{
+ int new_prs = cs->partition_root_state;
+ bool new_lb = (new_prs != PRS_ISOLATED);
+ bool rebuild_domains = (new_prs > 0) || (old_prs > 0);
+
+ if (new_lb != !!is_sched_load_balance(cs)) {
+ rebuild_domains = true;
+ if (new_lb)
+ set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+ else
+ clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+ }
+
+ if (rebuild_domains)
+ rebuild_sched_domains_locked();
+}
+
/**
* update_parent_subparts_cpumask - update subparts_cpus mask of parent cpuset
* @cs: The cpuset that requests change in partition root state
@@ -1336,8 +1380,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
return is_partition_invalid(parent)
? PERR_INVPARENT : PERR_NOTPART;
}
- if ((newmask && cpumask_empty(newmask)) ||
- (!newmask && cpumask_empty(cs->cpus_allowed)))
+ if (!newmask && cpumask_empty(cs->cpus_allowed))
return PERR_CPUSEMPTY;

/*
@@ -1403,11 +1446,16 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
cpumask_and(tmp->addmask, newmask, parent->cpus_allowed);
adding = cpumask_andnot(tmp->addmask, tmp->addmask,
parent->subparts_cpus);
+ /*
+ * Empty cpumask is not allewed
+ */
+ if (cpumask_empty(newmask)) {
+ part_error = PERR_CPUSEMPTY;
/*
* Make partition invalid if parent's effective_cpus could
* become empty and there are tasks in the parent.
*/
- if (adding &&
+ } else if (adding &&
cpumask_subset(parent->effective_cpus, tmp->addmask) &&
!cpumask_intersects(tmp->delmask, cpu_active_mask) &&
partition_is_populated(parent, cs)) {
@@ -1480,14 +1528,13 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,

/*
* Transitioning between invalid to valid or vice versa may require
- * changing CS_CPU_EXCLUSIVE and CS_SCHED_LOAD_BALANCE.
+ * changing CS_CPU_EXCLUSIVE.
*/
if (old_prs != new_prs) {
- if (is_prs_invalid(old_prs) && !is_cpu_exclusive(cs) &&
- (update_flag(CS_CPU_EXCLUSIVE, cs, 1) < 0))
- return PERR_NOTEXCL;
- if (is_prs_invalid(new_prs) && is_cpu_exclusive(cs))
- update_flag(CS_CPU_EXCLUSIVE, cs, 0);
+ int err = update_partition_exclusive(cs, new_prs);
+
+ if (err)
+ return err;
}

/*
@@ -1524,15 +1571,16 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
update_tasks_cpumask(parent, tmp->addmask);

/*
- * Set or clear CS_SCHED_LOAD_BALANCE when partcmd_update, if necessary.
- * rebuild_sched_domains_locked() may be called.
+ * For partcmd_update without newmask, it is being called from
+ * cpuset_hotplug_workfn() where cpus_read_lock() wasn't taken.
+ * Update the load balance flag and scheduling domain if
+ * cpus_read_trylock() is successful.
*/
- if (old_prs != new_prs) {
- if (old_prs == PRS_ISOLATED)
- update_flag(CS_SCHED_LOAD_BALANCE, cs, 1);
- else if (new_prs == PRS_ISOLATED)
- update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
+ if ((cmd == partcmd_update) && !newmask && cpus_read_trylock()) {
+ update_partition_sd_lb(cs, old_prs);
+ cpus_read_unlock();
}
+
notify_partition_change(cs, old_prs);
return 0;
}
@@ -1766,6 +1814,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
int retval;
struct tmpmasks tmp;
bool invalidate = false;
+ int old_prs = cs->partition_root_state;

/* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
if (cs == &top_cpuset)
@@ -1885,6 +1934,9 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
*/
if (parent->child_ecpus_count)
update_sibling_cpumasks(parent, cs, &tmp);
+
+ /* Update CS_SCHED_LOAD_BALANCE and/or sched_domains */
+ update_partition_sd_lb(cs, old_prs);
}
return 0;
}
@@ -2261,7 +2313,6 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
static int update_prstate(struct cpuset *cs, int new_prs)
{
int err = PERR_NONE, old_prs = cs->partition_root_state;
- bool sched_domain_rebuilt = false;
struct cpuset *parent = parent_cs(cs);
struct tmpmasks tmpmask;

@@ -2280,45 +2331,28 @@ static int update_prstate(struct cpuset *cs, int new_prs)
if (alloc_cpumasks(NULL, &tmpmask))
return -ENOMEM;

+ err = update_partition_exclusive(cs, new_prs);
+ if (err)
+ goto out;
+
if (!old_prs) {
/*
- * Turning on partition root requires setting the
- * CS_CPU_EXCLUSIVE bit implicitly as well and cpus_allowed
- * cannot be empty.
+ * cpus_allowed cannot be empty.
*/
if (cpumask_empty(cs->cpus_allowed)) {
err = PERR_CPUSEMPTY;
goto out;
}

- err = update_flag(CS_CPU_EXCLUSIVE, cs, 1);
- if (err) {
- err = PERR_NOTEXCL;
- goto out;
- }
-
err = update_parent_subparts_cpumask(cs, partcmd_enable,
NULL, &tmpmask);
- if (err) {
- update_flag(CS_CPU_EXCLUSIVE, cs, 0);
+ if (err)
goto out;
- }
-
- if (new_prs == PRS_ISOLATED) {
- /*
- * Disable the load balance flag should not return an
- * error unless the system is running out of memory.
- */
- update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
- sched_domain_rebuilt = true;
- }
} else if (old_prs && new_prs) {
/*
* A change in load balance state only, no change in cpumasks.
*/
- update_flag(CS_SCHED_LOAD_BALANCE, cs, (new_prs != PRS_ISOLATED));
- sched_domain_rebuilt = true;
- goto out; /* Sched domain is rebuilt in update_flag() */
+ goto out;
} else {
/*
* Switching back to member is always allowed even if it
@@ -2337,15 +2371,6 @@ static int update_prstate(struct cpuset *cs, int new_prs)
compute_effective_cpumask(cs->effective_cpus, cs, parent);
spin_unlock_irq(&callback_lock);
}
-
- /* Turning off CS_CPU_EXCLUSIVE will not return error */
- update_flag(CS_CPU_EXCLUSIVE, cs, 0);
-
- if (!is_sched_load_balance(cs)) {
- /* Make sure load balance is on */
- update_flag(CS_SCHED_LOAD_BALANCE, cs, 1);
- sched_domain_rebuilt = true;
- }
}

update_tasks_cpumask(parent, tmpmask.new_cpus);
@@ -2353,18 +2378,21 @@ static int update_prstate(struct cpuset *cs, int new_prs)
if (parent->child_ecpus_count)
update_sibling_cpumasks(parent, cs, &tmpmask);

- if (!sched_domain_rebuilt)
- rebuild_sched_domains_locked();
out:
/*
- * Make partition invalid if an error happen
+ * Make partition invalid & disable CS_CPU_EXCLUSIVE if an error
+ * happens.
*/
- if (err)
+ if (err) {
new_prs = -new_prs;
+ update_partition_exclusive(cs, new_prs);
+ }
+
spin_lock_irq(&callback_lock);
cs->partition_root_state = new_prs;
WRITE_ONCE(cs->prs_err, err);
spin_unlock_irq(&callback_lock);
+
/*
* Update child cpusets, if present.
* Force update if switching back to member.
@@ -2372,6 +2400,9 @@ static int update_prstate(struct cpuset *cs, int new_prs)
if (!list_empty(&cs->css.children))
update_cpumasks_hier(cs, &tmpmask, !new_prs);

+ /* Update sched domains and load balance flag */
+ update_partition_sd_lb(cs, old_prs);
+
notify_partition_change(cs, old_prs);
free_cpumasks(NULL, &tmpmask);
return 0;
--
2.31.1