[PATCH v5 2/6] cgroup/cpuset: Show invalid partition reason string

Waiman Long
2021-08-14T17:41:59Z

There are a number of different reasons which can cause a partition to
become invalid. A user seeing an invalid partition may not know exactly
why. To help user to get a better understanding of the underlying reason,
The cpuset.cpus.partition control file, when read, will now report the
reason why a partition become invalid. When a partition does become
invalid, reading the control file will show "root invalid (<reason>)"
where <reason> is a string that describes why the partition is invalid.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 46 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7705950ad70b..5fec3c96465c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -78,6 +78,24 @@ struct fmeter {
spinlock_t lock; /* guards read or write of above */
};

+/*
+ * Invalid partition error code
+ */
+enum prs_errcode {
+ PERR_NONE = 0,
+ PERR_INVCPUS,
+ PERR_NOCPUS,
+ PERR_PARENT,
+ PERR_HOTPLUG,
+};
+
+static const char * const perr_strings[] = {
+ [PERR_INVCPUS] = "Invalid change to cpuset.cpus",
+ [PERR_PARENT] = "Parent is no longer a partition root",
+ [PERR_NOCPUS] = "Parent unable to distribute cpu downstream",
+ [PERR_HOTPLUG] = "No cpu available due to hotplug",
+};
+
struct cpuset {
struct cgroup_subsys_state css;

@@ -163,6 +181,9 @@ struct cpuset {

/* Handle for cpuset.cpus.partition */
struct cgroup_file partition_file;
+
+ /* Invalid partiton error code, not lock protected */
+ enum prs_errcode prs_err;
};

/*
@@ -272,8 +293,13 @@ static inline int is_partition_root(const struct cpuset *cs)
static inline void notify_partition_change(struct cpuset *cs,
int old_prs, int new_prs)
{
- if (old_prs != new_prs)
- cgroup_file_notify(&cs->partition_file);
+ if (old_prs == new_prs)
+ return;
+ cgroup_file_notify(&cs->partition_file);
+
+ /* Reset prs_err if not invalid */
+ if (new_prs != PRS_ERROR)
+ WRITE_ONCE(cs->prs_err, PERR_NONE);
}

static struct cpuset top_cpuset = {
@@ -1243,6 +1269,8 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
cpu_active_mask))
part_error = true;
cpumask_copy(tmp->addmask, parent->effective_cpus);
+ if ((READ_ONCE(cpuset->prs_err) == PERR_NONE) && part_error)
+ WRITE_ONCE(cpuset->prs_err, PERR_INVCPUS);
}
} else {
/*
@@ -1264,6 +1292,8 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
part_error = (is_partition_root(cpuset) &&
!parent->nr_subparts_cpus) ||
cpumask_equal(tmp->addmask, parent->effective_cpus);
+ if (is_partition_root(cpuset) && part_error)
+ WRITE_ONCE(cpuset->prs_err, PERR_NOCPUS);
}

if (cmd == partcmd_update) {
@@ -1427,6 +1457,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
* When parent is invalid, it has to be too.
*/
new_prs = PRS_ERROR;
+ WRITE_ONCE(cp->prs_err, PERR_PARENT);
break;
}
}
@@ -2551,6 +2582,7 @@ static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
static int sched_partition_show(struct seq_file *seq, void *v)
{
struct cpuset *cs = css_cs(seq_css(seq));
+ const char *err;

switch (cs->partition_root_state) {
case PRS_ENABLED:
@@ -2560,7 +2592,11 @@ static int sched_partition_show(struct seq_file *seq, void *v)
seq_puts(seq, "member\n");
break;
case PRS_ERROR:
- seq_puts(seq, "root invalid\n");
+ err = perr_strings[READ_ONCE(cs->prs_err)];
+ if (err)
+ seq_printf(seq, "root invalid (%s)\n", err);
+ else
+ seq_puts(seq, "root invalid\n");
break;
}
return 0;
@@ -3160,6 +3196,10 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
spin_lock_irq(&callback_lock);
cs->partition_root_state = PRS_ERROR;
spin_unlock_irq(&callback_lock);
+ if (parent->partition_root_state == PRS_ERROR)
+ WRITE_ONCE(cs->prs_err, PERR_PARENT);
+ else
+ WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
notify_partition_change(cs, old_prs, PRS_ERROR);
}
cpuset_force_rebuild();
--
2.18.1