Subject: [PATCH 16/31] PCI: Flush PCI probe workqueue on cpuset isolated partition change

From: Frederic Weisbecker <[email-masked]>
Date: Wed, 5 Nov 2025 22:03:32 +0100

The HK_TYPE_DOMAIN housekeeping cpumask is now modifiable at runtime. In
order to synchronize against PCI probe works and make sure that no
asynchronous probing is still pending or executing on a newly isolated
CPU, the housekeeping subsystem must flush the PCI probe works.

However the PCI probe works can't be flushed easily since they are
queued to the main per-CPU workqueue pool.

Solve this with creating a PCI probe-specific pool and provide and use
the appropriate flushing API.

Signed-off-by: Frederic Weisbecker <[email-masked]>
---
 drivers/pci/pci-driver.c | 17 ++++++++++++++++-
 include/linux/pci.h      |  3 +++
 kernel/sched/isolation.c |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 7b74d22b20f7..ac86aaec8bcf 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -337,6 +337,8 @@ static int local_pci_probe(struct drv_dev_and_id *ddi)
 	return 0;
 }
 
+static struct workqueue_struct *pci_probe_wq;
+
 struct pci_probe_arg {
 	struct drv_dev_and_id *ddi;
 	struct work_struct work;
@@ -407,7 +409,11 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 		cpu = cpumask_any_and(cpumask_of_node(node),
 				      wq_domain_mask);
 		if (cpu < nr_cpu_ids) {
-			schedule_work_on(cpu, &arg.work);
+			struct workqueue_struct *wq = pci_probe_wq;
+
+			if (WARN_ON_ONCE(!wq))
+				wq = system_percpu_wq;
+			queue_work_on(cpu, wq, &arg.work);
 			rcu_read_unlock();
 			flush_work(&arg.work);
 			error = arg.ret;
@@ -425,6 +431,11 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 	return error;
 }
 
+void pci_probe_flush_workqueue(void)
+{
+	flush_workqueue(pci_probe_wq);
+}
+
 /**
  * __pci_device_probe - check if a driver wants to claim a specific PCI device
  * @drv: driver to call to check if it wants the PCI device
@@ -1760,6 +1771,10 @@ static int __init pci_driver_init(void)
 {
 	int ret;
 
+	pci_probe_wq = alloc_workqueue("sync_wq", WQ_PERCPU, 0);
+	if (!pci_probe_wq)
+		return -ENOMEM;
+
 	ret = bus_register(&pci_bus_type);
 	if (ret)
 		return ret;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d1fdf81fbe1e..3281c235b895 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1175,6 +1175,7 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 				    struct pci_ops *ops, void *sysdata,
 				    struct list_head *resources);
 int pci_host_probe(struct pci_host_bridge *bridge);
+void pci_probe_flush_workqueue(void);
 int pci_bus_insert_busn_res(struct pci_bus *b, int bus, int busmax);
 int pci_bus_update_busn_res_end(struct pci_bus *b, int busmax);
 void pci_bus_release_busn_res(struct pci_bus *b);
@@ -2037,6 +2038,8 @@ static inline int pci_has_flag(int flag) { return 0; }
 _PCI_NOP_ALL(read, *)
 _PCI_NOP_ALL(write,)
 
+static inline void pci_probe_flush_workqueue(void) { }
+
 static inline struct pci_dev *pci_get_device(unsigned int vendor,
 					     unsigned int device,
 					     struct pci_dev *from)
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 8338c9259f4f..303cc3419ecb 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -8,6 +8,7 @@
  *
  */
 #include <linux/sched/isolation.h>
+#include <linux/pci.h>
 #include "sched.h"
 
 enum hk_flags {
@@ -145,6 +146,7 @@ int housekeeping_update(struct cpumask *mask, enum hk_type type)
 
 	synchronize_rcu();
 
+	pci_probe_flush_workqueue();
 	mem_cgroup_flush_workqueue();
 	vmstat_flush_workqueue();
 
-- 
2.51.0