[PATCH RFC v2 09/19] fs/resctrl: Take memory hotplug lock whenever taking CPU hotplug lock

[Fenghua Yu]

From: James Morse <james.morse at arm.com>

resctrl takes the read side CPU hotplug lock whenever it is working
with the list of domains. This prevents a CPU being brought online
and the list being modified while resctrl is walking the list, or
picking CPUs from the CPU masks.

If resctrl domains for CPU-less NUMA nodes are to be supported, this
would not be enough to prevent the domain list form being modified as
a NUMA node can come online with only memory.

Take the memory hotplug lock whenever the CPU hotplug lock is taken.

Signed-off-by: James Morse <james.morse at arm.com>
Signed-off-by: Fenghua Yu <fenghuay at nvidia.com>
---
 fs/resctrl/pseudo_lock.c |  3 +++
 fs/resctrl/rdtgroup.c    | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/fs/resctrl/pseudo_lock.c b/fs/resctrl/pseudo_lock.c
index 17b99a075eaf..c865913cb534 100644
--- a/fs/resctrl/pseudo_lock.c
+++ b/fs/resctrl/pseudo_lock.c
@@ -16,6 +16,7 @@
 #include <linux/cpumask.h>
 #include <linux/debugfs.h>
 #include <linux/kthread.h>
+#include <linux/memory_hotplug.h>
 #include <linux/mman.h>
 #include <linux/pm_qos.h>
 #include <linux/resctrl.h>
@@ -718,6 +719,7 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
 	int ret = -1;
 
 	cpus_read_lock();
+	get_online_mems();
 	mutex_lock(&rdtgroup_mutex);
 
 	if (rdtgrp->flags & RDT_DELETED) {
@@ -765,6 +767,7 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
 
 out:
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 	return ret;
 }
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index d60868f7d5e7..a16e35b587c4 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -18,6 +18,7 @@
 #include <linux/fs_parser.h>
 #include <linux/sysfs.h>
 #include <linux/kernfs.h>
+#include <linux/memory_hotplug.h>
 #include <linux/once.h>
 #include <linux/resctrl.h>
 #include <linux/seq_buf.h>
@@ -3238,6 +3239,7 @@ struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
 	rdtgroup_kn_get(rdtgrp, kn);
 
 	cpus_read_lock();
+	get_online_mems();
 	mutex_lock(&rdtgroup_mutex);
 	rdt_last_cmd_clear();
 
@@ -3265,6 +3267,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 		return;
 
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 
 	rdtgroup_kn_put(rdtgrp, kn);
@@ -3299,6 +3302,7 @@ bool info_kn_lock(struct kernfs_node *kn)
 {
 	kernfs_break_active_protection(kn);
 	cpus_read_lock();
+	get_online_mems();
 	mutex_lock(&rdtgroup_mutex);
 
 	/*
@@ -3307,6 +3311,7 @@ bool info_kn_lock(struct kernfs_node *kn)
 	 */
 	if (!rdtgroup_default.kn || !is_active_resctrl_node(kn)) {
 		mutex_unlock(&rdtgroup_mutex);
+		put_online_mems();
 		cpus_read_unlock();
 		kernfs_unbreak_active_protection(kn);
 		return false;
@@ -3318,6 +3323,7 @@ bool info_kn_lock(struct kernfs_node *kn)
 void info_kn_unlock(struct kernfs_node *kn)
 {
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 	kernfs_unbreak_active_protection(kn);
 }
@@ -3671,6 +3677,7 @@ static void resctrl_unmount(void)
 	struct rdt_resource *r;
 
 	cpus_read_lock();
+	get_online_mems();
 	mutex_lock(&rdtgroup_mutex);
 
 	rdt_disable_ctx();
@@ -3686,6 +3693,7 @@ static void resctrl_unmount(void)
 		resctrl_arch_disable_mon();
 	resctrl_mounted = false;
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 }
 
@@ -3701,6 +3709,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	DO_ONCE_SLEEPABLE(resctrl_arch_pre_mount);
 
 	cpus_read_lock();
+	get_online_mems();
 	mutex_lock(&rdtgroup_mutex);
 	/*
 	 * resctrl file system can only be mounted once.
@@ -3804,6 +3813,7 @@ static int rdt_get_tree(struct fs_context *fc)
 
 	rdt_last_cmd_clear();
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 
 	ret = kernfs_get_tree(fc);
@@ -3836,6 +3846,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	rdtgroup_destroy_root();
 out:
 	mutex_unlock(&rdtgroup_mutex);
+	put_online_mems();
 	cpus_read_unlock();
 	return ret;
 }
@@ -5502,12 +5513,14 @@ static bool resctrl_online_domains_exist(void)
 void resctrl_exit(void)
 {
 	cpus_read_lock();
+	get_online_mems();
 	WARN_ON_ONCE(resctrl_online_domains_exist());
 
 	mutex_lock(&rdtgroup_mutex);
 	resctrl_fs_teardown();
 	mutex_unlock(&rdtgroup_mutex);
 
+	put_online_mems();
 	cpus_read_unlock();
 
 	debugfs_remove_recursive(debugfs_resctrl);
-- 
2.53.0