Re: [PATCH 01/33] PCI: Prepare to protect against concurrent isolated cpuset change

Bjorn Helgaas
2026-01-22T16:14:22Z

On Thu, Jan 01, 2026 at 11:13:26PM +0100, Frederic Weisbecker wrote:
> HK_TYPE_DOMAIN will soon integrate cpuset isolated partitions and
> therefore be made modifiable at runtime. Synchronize against the cpumask
> update using RCU.
>
> The RCU locked section includes both the housekeeping CPU target
> election for the PCI probe work and the work enqueue.
>
> This way the housekeeping update side will simply need to flush the
> pending related works after updating the housekeeping mask in order to
> make sure that no PCI work ever executes on an isolated CPU. This part
> will be handled in a subsequent patch.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

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

> ---
> drivers/pci/pci-driver.c | 47 ++++++++++++++++++++++++++++++++--------
> 1 file changed, 38 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 7c2d9d596258..a6111140755c 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -302,9 +302,8 @@ struct drv_dev_and_id {
> const struct pci_device_id *id;
> };
>
> -static long local_pci_probe(void *_ddi)
> +static int local_pci_probe(struct drv_dev_and_id *ddi)
> {
> - struct drv_dev_and_id *ddi = _ddi;
> struct pci_dev *pci_dev = ddi->dev;
> struct pci_driver *pci_drv = ddi->drv;
> struct device *dev = &pci_dev->dev;
> @@ -338,6 +337,19 @@ static long local_pci_probe(void *_ddi)
> return 0;
> }
>
> +struct pci_probe_arg {
> + struct drv_dev_and_id *ddi;
> + struct work_struct work;
> + int ret;
> +};
> +
> +static void local_pci_probe_callback(struct work_struct *work)
> +{
> + struct pci_probe_arg *arg = container_of(work, struct pci_probe_arg, work);
> +
> + arg->ret = local_pci_probe(arg->ddi);
> +}
> +
> static bool pci_physfn_is_probed(struct pci_dev *dev)
> {
> #ifdef CONFIG_PCI_IOV
> @@ -362,34 +374,51 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
> dev->is_probed = 1;
>
> cpu_hotplug_disable();
> -
> /*
> * Prevent nesting work_on_cpu() for the case where a Virtual Function
> * device is probed from work_on_cpu() of the Physical device.
> */
> if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
> pci_physfn_is_probed(dev)) {
> - cpu = nr_cpu_ids;
> + error = local_pci_probe(&ddi);
> } else {
> cpumask_var_t wq_domain_mask;
> + struct pci_probe_arg arg = { .ddi = &ddi };
>
> if (!zalloc_cpumask_var(&wq_domain_mask, GFP_KERNEL)) {
> error = -ENOMEM;
> goto out;
> }
> +
> + INIT_WORK_ONSTACK(&arg.work, local_pci_probe_callback);
> +
> + /*
> + * The target election and the enqueue of the work must be within
> + * the same RCU read side section so that when the workqueue pool
> + * is flushed after a housekeeping cpumask update, further readers
> + * are guaranteed to queue the probing work to the appropriate
> + * targets.
> + */
> + rcu_read_lock();
> cpumask_and(wq_domain_mask,
> housekeeping_cpumask(HK_TYPE_WQ),
> housekeeping_cpumask(HK_TYPE_DOMAIN));
>
> cpu = cpumask_any_and(cpumask_of_node(node),
> wq_domain_mask);
> + if (cpu < nr_cpu_ids) {
> + schedule_work_on(cpu, &arg.work);
> + rcu_read_unlock();
> + flush_work(&arg.work);
> + error = arg.ret;
> + } else {
> + rcu_read_unlock();
> + error = local_pci_probe(&ddi);
> + }
> +
> free_cpumask_var(wq_domain_mask);
> + destroy_work_on_stack(&arg.work);
> }
> -
> - if (cpu < nr_cpu_ids)
> - error = work_on_cpu(cpu, local_pci_probe, &ddi);
> - else
> - error = local_pci_probe(&ddi);
> out:
> dev->is_probed = 0;
> cpu_hotplug_enable();
> --
> 2.51.1
>