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Commit 67546762 authored by Yijing Wang's avatar Yijing Wang Committed by Bjorn Helgaas
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PCI: Protect pci_bus->slots with pci_slot_mutex, not pci_bus_sem 

Rajat Jain reported a deadlock when PCIe hot-add and AER recovery happen at
the same time:

thread 1:

  pciehp_enable_slot
    pciehp_configure_device
      pci_bus_add_devices
        pci_bus_add_device
          device_attach
            device_lock(dev)                       # acquire device lock
            ...
            pciehp_probe
              init_slot
                pci_hp_register
                  pci_create_slot
                    down_write(pci_bus_sem)        # deadlock here

thread 2:

  aer_isr_one_error
    aer_process_err_device
      do_recovery
        broadcast_error_message(..., report_error_detected)
          pci_walk_bus(..., cb=report_error_detected, ...)
            down_read(&pci_bus_sem)                # acquire pci_bus_sem
            report_error_detected(dev)             # cb()
              device_lock(dev)                     # deadlock here

Previously, the bus->devices and bus->slots list were protected by
pci_bus_sem.  In pci_create_slot(), we held it for writing so we could
add to the bus->slots list.

Add a new local pci_slot_mutex to protect bus->slots.  Hold pci_bus_sem for
reading while searching the bus->devices list.

[bhelgaas: changelog]
Link: http://lkml.kernel.org/r/CAA93t1qpPqbih+UB0McA_d_+2rVaNkXsinAUxYzK9+JXSS+L-g@mail.gmail.com


Reported-by: default avatarRajat Jain <rajatja@google.com>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarYijing Wang <wangyijing@huawei.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
parent ac10836b

drivers/pci/slot.c

+11 −7
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 


struct kset *pci_slots_kset;

EXPORT_SYMBOL_GPL(pci_slots_kset);

static DEFINE_MUTEX(pci_slot_mutex);



static ssize_t pci_slot_attr_show(struct kobject *kobj,

					struct attribute *attr, char *buf)
@@ -106,9 +107,11 @@ static void pci_slot_release(struct kobject *kobj) 
	dev_dbg(&slot->bus->dev, "dev %02x, released physical slot %s\n",

		slot->number, pci_slot_name(slot));



	down_read(&pci_bus_sem);

	list_for_each_entry(dev, &slot->bus->devices, bus_list)

		if (PCI_SLOT(dev->devfn) == slot->number)

			dev->slot = NULL;

	up_read(&pci_bus_sem);



	list_del(&slot->list);
@@ -194,9 +197,8 @@ static int rename_slot(struct pci_slot *slot, const char *name) 
static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)

{

	struct pci_slot *slot;

	/*

	 * We already hold pci_bus_sem so don't worry

	 */



	/* We already hold pci_slot_mutex */

	list_for_each_entry(slot, &parent->slots, list)

		if (slot->number == slot_nr) {

			kobject_get(&slot->kobj);
@@ -253,7 +255,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, 
	int err = 0;

	char *slot_name = NULL;



	down_write(&pci_bus_sem);

	mutex_lock(&pci_slot_mutex);



	if (slot_nr == -1)

		goto placeholder;
@@ -301,16 +303,18 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr, 
	INIT_LIST_HEAD(&slot->list);

	list_add(&slot->list, &parent->slots);



	down_read(&pci_bus_sem);

	list_for_each_entry(dev, &parent->devices, bus_list)

		if (PCI_SLOT(dev->devfn) == slot_nr)

			dev->slot = slot;

	up_read(&pci_bus_sem);



	dev_dbg(&parent->dev, "dev %02x, created physical slot %s\n",

		slot_nr, pci_slot_name(slot));



out:

	kfree(slot_name);

	up_write(&pci_bus_sem);

	mutex_unlock(&pci_slot_mutex);

	return slot;

err:

	kfree(slot);
@@ -332,9 +336,9 @@ void pci_destroy_slot(struct pci_slot *slot) 
	dev_dbg(&slot->bus->dev, "dev %02x, dec refcount to %d\n",

		slot->number, atomic_read(&slot->kobj.kref.refcount) - 1);



	down_write(&pci_bus_sem);

	mutex_lock(&pci_slot_mutex);

	kobject_put(&slot->kobj);

	up_write(&pci_bus_sem);

	mutex_unlock(&pci_slot_mutex);

}

EXPORT_SYMBOL_GPL(pci_destroy_slot);

include/linux/pci.h

+2 −1
Original line number Diff line number Diff line
@@ -446,7 +446,8 @@ struct pci_bus { 
	struct list_head children;	/* list of child buses */

	struct list_head devices;	/* list of devices on this bus */

	struct pci_dev	*self;		/* bridge device as seen by parent */

	struct list_head slots;		/* list of slots on this bus */

	struct list_head slots;		/* list of slots on this bus;

					   protected by pci_slot_mutex */

	struct resource *resource[PCI_BRIDGE_RESOURCE_NUM];

	struct list_head resources;	/* address space routed to this bus */

	struct resource busn_res;	/* bus numbers routed to this bus */