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Subject[ 051/128] PCI: shpchp: Use per-slot workqueues to avoid deadlock
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bjorn Helgaas <bhelgaas@google.com>

commit f652e7d2916fe2fcf9e7d709aa5b7476b431e2dd upstream.

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/pci/hotplug/shpchp.h | 2 +-
drivers/pci/hotplug/shpchp_core.c | 26 ++++++++++++++------------
drivers/pci/hotplug/shpchp_ctrl.c | 6 +++---
3 files changed, 18 insertions(+), 16 deletions(-)

--- a/drivers/pci/hotplug/shpchp.h
+++ b/drivers/pci/hotplug/shpchp.h
@@ -46,7 +46,6 @@
extern int shpchp_poll_mode;
extern int shpchp_poll_time;
extern int 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;
};

--- a/drivers/pci/hotplug/shpchp_core.c
+++ b/drivers/pci/hotplug/shpchp_core.c
@@ -39,7 +39,6 @@
int shpchp_debug;
int 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>"
@@ -122,6 +121,14 @@ static int init_slots(struct controller
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);

@@ -141,7 +148,7 @@ static int init_slots(struct controller
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);
@@ -153,6 +160,8 @@ static int init_slots(struct controller
}

return 0;
+error_slotwq:
+ destroy_workqueue(slot->wq);
error_info:
kfree(info);
error_hpslot:
@@ -173,7 +182,7 @@ void cleanup_slots(struct controller *ct
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);
}
}
@@ -356,18 +365,12 @@ static struct pci_driver shpc_driver = {

static int __init shpcd_init(void)
{
- int retval = 0;
-
- shpchp_wq = alloc_ordered_workqueue("shpchp", 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;
}

@@ -375,7 +378,6 @@ 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");
}

--- a/drivers/pci/hotplug/shpchp_ctrl.c
+++ b/drivers/pci/hotplug/shpchp_ctrl.c
@@ -51,7 +51,7 @@ static int queue_interrupt_event(struct
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;
}
@@ -456,7 +456,7 @@ void shpchp_queue_pushbutton_work(struct
kfree(info);
goto out;
}
- queue_work(shpchp_wq, &info->work);
+ queue_work(p_slot->wq, &info->work);
out:
mutex_unlock(&p_slot->lock);
}
@@ -504,7 +504,7 @@ static void handle_button_press_event(st
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:



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