[RFC PATCH v5 6/7] fs/resctrl: Call architecture hooks for every mount/unmount

Tony Luck
2026-04-10T20:05:45Z

Architecture code for AET needs to acquire INTEL_PMT_TELEMETRY module
references on mount and release them on unmount.

Add hooks for every mount/unmount of the resctrl file system so that
architecture code can allocate on mount and free on unmount.

Add resctrl_mount_lock to protect mount/unmount operations and write access
to "resctrl_mounted". This simplifies the code flow around the repeat mount
with -EBUSY return to avoid calling resctrl_arch_pre_mount() when the file
system is mounted.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
include/linux/resctrl.h | 9 ++++++---
fs/resctrl/rdtgroup.c | 35 ++++++++++++++++++++++++++++-------
2 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index f3eb6dfa61d4..f3da533e182c 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -551,12 +551,15 @@ void resctrl_online_cpu(unsigned int cpu);
void resctrl_offline_cpu(unsigned int cpu);

/*
- * Architecture hook called at beginning of first file system mount attempt.
- * No locks are held.
+ * Architecture hook called before attempting to mount the file system.
+ * Called with just resctrl_mount_lock held.
*/
void resctrl_arch_pre_mount(void);

-/* Called to report unmount. */
+/*
+ * Architecture hook called when mount fails, or on unmount.
+ * Called with just resctrl_mount_lock held.
+ */
void resctrl_arch_unmount(void);

/**
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5da305bd36c9..444bc359e4a7 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -18,7 +18,6 @@
#include <linux/fs_parser.h>
#include <linux/sysfs.h>
#include <linux/kernfs.h>
-#include <linux/once.h>
#include <linux/resctrl.h>
#include <linux/seq_buf.h>
#include <linux/seq_file.h>
@@ -48,7 +47,14 @@ LIST_HEAD(resctrl_schema_all);
*/
static LIST_HEAD(mon_data_kn_priv_list);

-/* The filesystem can only be mounted once. */
+/* Mutex protecting mount/unmount operations */
+static DEFINE_MUTEX(resctrl_mount_lock);
+
+/*
+ * The filesystem can only be mounted once.
+ * Updated with both rdtgroup_mutex and resctrl_mount_lock held.
+ * Safe to read while holding either rdtgroup_mutex or resctrl_mount_lock.
+ */
bool resctrl_mounted;

/* Kernel fs node for "info" directory under root */
@@ -2788,18 +2794,21 @@ static int rdt_get_tree(struct fs_context *fc)
struct rdt_resource *r;
int ret;

- DO_ONCE_SLEEPABLE(resctrl_arch_pre_mount);
+ mutex_lock(&resctrl_mount_lock);

- cpus_read_lock();
- mutex_lock(&rdtgroup_mutex);
/*
* resctrl file system can only be mounted once.
*/
if (resctrl_mounted) {
- ret = -EBUSY;
- goto out;
+ mutex_unlock(&resctrl_mount_lock);
+ return -EBUSY;
}

+ resctrl_arch_pre_mount();
+
+ cpus_read_lock();
+ mutex_lock(&rdtgroup_mutex);
+
ret = setup_rmid_lru_list();
if (ret)
goto out;
@@ -2897,6 +2906,12 @@ static int rdt_get_tree(struct fs_context *fc)
rdt_last_cmd_clear();
mutex_unlock(&rdtgroup_mutex);
cpus_read_unlock();
+
+ if (ret)
+ resctrl_arch_unmount();
+
+ mutex_unlock(&resctrl_mount_lock);
+
return ret;
}

@@ -3169,6 +3184,8 @@ static void rdt_kill_sb(struct super_block *sb)
{
struct rdt_resource *r;

+ mutex_lock(&resctrl_mount_lock);
+
cpus_read_lock();
mutex_lock(&rdtgroup_mutex);

@@ -3187,6 +3204,10 @@ static void rdt_kill_sb(struct super_block *sb)
kernfs_kill_sb(sb);
mutex_unlock(&rdtgroup_mutex);
cpus_read_unlock();
+
+ resctrl_arch_unmount();
+
+ mutex_unlock(&resctrl_mount_lock);
}

static struct file_system_type rdt_fs_type = {
--
2.53.0