Re: [PATCH 17/33] PCI: Flush PCI probe workqueue on cpuset isolated partition change

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jan 01, 2026 at 11:13:42PM +0100, Frederic Weisbecker wrote:
> 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 <frederic@kernel.org>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  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 a6111140755c..b902d8adf9a5 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
> @@ -1762,6 +1773,10 @@ 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 864775651c6f..f14f467e50de 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1206,6 +1206,7 @@ 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);
> @@ -2079,6 +2080,8 @@ 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 ec3f15164fd1..5239f556745d 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 {
> @@ -142,6 +143,7 @@ int housekeeping_update(struct cpumask *isol_mask)
>  
>  	synchronize_rcu();
>  
> +	pci_probe_flush_workqueue();
>  	mem_cgroup_flush_workqueue();
>  	vmstat_flush_workqueue();
>  
> -- 
> 2.51.1
>