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PCI: shpchp: Use per-slot workqueues to avoid deadlock 

When we have an SHPC-capable bridge with a second SHPC-capable bridge
below it, pushing the upstream bridge's attention button causes a
deadlock.

The deadlock happens because we use the shpchp_wq workqueue to run
shpchp_pushbutton_thread(), which uses shpchp_disable_slot() to remove
devices below the upstream bridge.  When we remove the downstream bridge,
we call shpc_remove(), the shpchp driver's .remove() method.  That calls
flush_workqueue(shpchp_wq), which deadlocks because the
shpchp_pushbutton_thread() work item is still running.

This patch avoids the deadlock by creating a workqueue for every slot
and removing the single shared workqueue.

Here's the call path that leads to the deadlock:

  shpchp_queue_pushbutton_work
    queue_work(shpchp_wq)		# shpchp_pushbutton_thread
    ...

  shpchp_pushbutton_thread
    shpchp_disable_slot
      remove_board
        shpchp_unconfigure_device
          pci_stop_and_remove_bus_device
            ...
              shpc_remove		# shpchp driver .remove method
                hpc_release_ctlr
                  cleanup_slots
                    flush_workqueue(shpchp_wq)

This change is based on code inspection, since we don't have hardware
with this topology.

Based-on-patch-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org
This commit is contained in:
Bjorn Helgaas 2013-01-11 12:21:15 -07:00
parent d347e75847
commit f652e7d291
3 changed files with 18 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/pci/hotplug/shpchp.h
View File

@ -46,7 +46,6 @@
extern bool shpchp_poll_mode;
extern int shpchp_poll_time;
extern bool shpchp_debug;
extern struct workqueue_struct *shpchp_wq;
#define dbg(format, arg...) \
do { \
@ -90,6 +89,7 @@ struct slot {
struct list_head slot_list;
struct delayed_work work; /* work for button event */
struct mutex lock;
struct workqueue_struct *wq;
u8 hp_slot;
};

26
drivers/pci/hotplug/shpchp_core.c
View File

@ -39,7 +39,6 @@
bool shpchp_debug;
bool shpchp_poll_mode;
int shpchp_poll_time;
struct workqueue_struct *shpchp_wq;
#define DRIVER_VERSION "0.4"
#define DRIVER_AUTHOR "Dan Zink <dan.zink@compaq.com>, Greg Kroah-Hartman <greg@kroah.com>, Dely Sy <dely.l.sy@intel.com>"
@ -128,6 +127,14 @@ static int init_slots(struct controller *ctrl)
slot->device = ctrl->slot_device_offset + i;
slot->hpc_ops = ctrl->hpc_ops;
slot->number = ctrl->first_slot + (ctrl->slot_num_inc * i);
snprintf(name, sizeof(name), "shpchp-%d", slot->number);
slot->wq = alloc_workqueue(name, 0, 0);
if (!slot->wq) {
retval = -ENOMEM;
goto error_info;
}
mutex_init(&slot->lock);
INIT_DELAYED_WORK(&slot->work, shpchp_queue_pushbutton_work);
@ -147,7 +154,7 @@ static int init_slots(struct controller *ctrl)
if (retval) {
ctrl_err(ctrl, "pci_hp_register failed with error %d\n",
retval);
goto error_info;
goto error_slotwq;
}
get_power_status(hotplug_slot, &info->power_status);
@ -159,6 +166,8 @@ static int init_slots(struct controller *ctrl)
}
return 0;
error_slotwq:
destroy_workqueue(slot->wq);
error_info:
kfree(info);
error_hpslot:
@ -179,7 +188,7 @@ void cleanup_slots(struct controller *ctrl)
slot = list_entry(tmp, struct slot, slot_list);
list_del(&slot->slot_list);
cancel_delayed_work(&slot->work);
flush_workqueue(shpchp_wq);
destroy_workqueue(slot->wq);
pci_hp_deregister(slot->hotplug_slot);
}
}
@ -362,18 +371,12 @@ static struct pci_driver shpc_driver = {
static int __init shpcd_init(void)
{
int retval = 0;
shpchp_wq = alloc_workqueue("shpchp", 0, 0);
if (!shpchp_wq)
return -ENOMEM;
int retval;
retval = pci_register_driver(&shpc_driver);
dbg("%s: pci_register_driver = %d\n", __func__, retval);
info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
if (retval) {
destroy_workqueue(shpchp_wq);
}
return retval;
}
@ -381,7 +384,6 @@ static void __exit shpcd_cleanup(void)
{
dbg("unload_shpchpd()\n");
pci_unregister_driver(&shpc_driver);
destroy_workqueue(shpchp_wq);
info(DRIVER_DESC " version: " DRIVER_VERSION " unloaded\n");
}

6
drivers/pci/hotplug/shpchp_ctrl.c
View File

@ -51,7 +51,7 @@ static int queue_interrupt_event(struct slot *p_slot, u32 event_type)
info->p_slot = p_slot;
INIT_WORK(&info->work, interrupt_event_handler);
queue_work(shpchp_wq, &info->work);
queue_work(p_slot->wq, &info->work);
return 0;
}
@ -453,7 +453,7 @@ void shpchp_queue_pushbutton_work(struct work_struct *work)
kfree(info);
goto out;
}
queue_work(shpchp_wq, &info->work);
queue_work(p_slot->wq, &info->work);
out:
mutex_unlock(&p_slot->lock);
}
@ -501,7 +501,7 @@ static void handle_button_press_event(struct slot *p_slot)
p_slot->hpc_ops->green_led_blink(p_slot);
p_slot->hpc_ops->set_attention_status(p_slot, 0);
queue_delayed_work(shpchp_wq, &p_slot->work, 5*HZ);
queue_delayed_work(p_slot->wq, &p_slot->work, 5*HZ);
break;
case BLINKINGOFF_STATE:
case BLINKINGON_STATE: