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Subject[ 047/128] PCI: pciehp: Use per-slot workqueues to avoid deadlock
3.2-stable review patch.  If anyone has any objections, please let me know.

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

From: Yijing Wang <wangyijing@huawei.com>

commit c2be6f93b383c873a4f9d521afa49b1b67d06085 upstream.

When we have a hotplug-capable PCIe port with a second hotplug-capable
PCIe port below it, removing the device below the upstream port causes
a deadlock.

The deadlock happens because we use the pciehp_wq workqueue to run
pciehp_power_thread(), which uses pciehp_disable_slot() to remove devices
below the upstream port. When we remove the downstream PCIe port, we call
pciehp_remove(), the pciehp driver's .remove() method. That calls
flush_workqueue(pciehp_wq), which deadlocks because the
pciehp_power_thread() work item is still running.

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

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

pciehp_queue_pushbutton_work
queue_work(pciehp_wq) # queue pciehp_power_thread
...

pciehp_power_thread
pciehp_disable_slot
remove_board
pciehp_unconfigure_device
pci_stop_and_remove_bus_device
...
pciehp_remove # pciehp driver .remove method
pciehp_release_ctrl
pcie_cleanup_slot
flush_workqueue(pciehp_wq)

This is fairly urgent because it can be caused by simply unplugging a
Thunderbolt adapter, as reported by Daniel below.

[bhelgaas: changelog]
Reference: http://lkml.kernel.org/r/CAMVG2ssiRgcTD1bej2tkUUfsWmpL5eNtPcNif9va2-Gzb2u8nQ@mail.gmail.com
Reported-and-tested-by: Daniel J Blueman <daniel@quora.org>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-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/pciehp.h | 2 +-
drivers/pci/hotplug/pciehp_core.c | 11 ++---------
drivers/pci/hotplug/pciehp_ctrl.c | 8 ++++----
drivers/pci/hotplug/pciehp_hpc.c | 11 ++++++++++-
4 files changed, 17 insertions(+), 15 deletions(-)

--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -44,7 +44,6 @@ extern int pciehp_poll_mode;
extern int pciehp_poll_time;
extern int pciehp_debug;
extern int pciehp_force;
-extern struct workqueue_struct *pciehp_wq;

#define dbg(format, arg...) \
do { \
@@ -78,6 +77,7 @@ struct slot {
struct hotplug_slot *hotplug_slot;
struct delayed_work work; /* work for button event */
struct mutex lock;
+ struct workqueue_struct *wq;
};

struct event_info {
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -42,7 +42,6 @@ int pciehp_debug;
int pciehp_poll_mode;
int pciehp_poll_time;
int pciehp_force;
-struct workqueue_struct *pciehp_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>"
@@ -340,18 +339,13 @@ static int __init pcied_init(void)
{
int retval = 0;

- pciehp_wq = alloc_workqueue("pciehp", 0, 0);
- if (!pciehp_wq)
- return -ENOMEM;
-
pciehp_firmware_init();
retval = pcie_port_service_register(&hpdriver_portdrv);
dbg("pcie_port_service_register = %d\n", retval);
info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
- if (retval) {
- destroy_workqueue(pciehp_wq);
+ if (retval)
dbg("Failure to register service\n");
- }
+
return retval;
}

@@ -359,7 +353,6 @@ static void __exit pcied_cleanup(void)
{
dbg("unload_pciehpd()\n");
pcie_port_service_unregister(&hpdriver_portdrv);
- destroy_workqueue(pciehp_wq);
info(DRIVER_DESC " version: " DRIVER_VERSION " unloaded\n");
}

--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -49,7 +49,7 @@ static int queue_interrupt_event(struct
info->p_slot = p_slot;
INIT_WORK(&info->work, interrupt_event_handler);

- queue_work(pciehp_wq, &info->work);
+ queue_work(p_slot->wq, &info->work);

return 0;
}
@@ -344,7 +344,7 @@ void pciehp_queue_pushbutton_work(struct
kfree(info);
goto out;
}
- queue_work(pciehp_wq, &info->work);
+ queue_work(p_slot->wq, &info->work);
out:
mutex_unlock(&p_slot->lock);
}
@@ -377,7 +377,7 @@ static void handle_button_press_event(st
if (ATTN_LED(ctrl))
pciehp_set_attention_status(p_slot, 0);

- queue_delayed_work(pciehp_wq, &p_slot->work, 5*HZ);
+ queue_delayed_work(p_slot->wq, &p_slot->work, 5*HZ);
break;
case BLINKINGOFF_STATE:
case BLINKINGON_STATE:
@@ -439,7 +439,7 @@ static void handle_surprise_event(struct
else
p_slot->state = POWERON_STATE;

- queue_work(pciehp_wq, &info->work);
+ queue_work(p_slot->wq, &info->work);
}

static void interrupt_event_handler(struct work_struct *work)
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -789,23 +789,32 @@ static void pcie_shutdown_notification(s
static int pcie_init_slot(struct controller *ctrl)
{
struct slot *slot;
+ char name[32];

slot = kzalloc(sizeof(*slot), GFP_KERNEL);
if (!slot)
return -ENOMEM;

+ snprintf(name, sizeof(name), "pciehp-%u", PSN(ctrl));
+ slot->wq = alloc_workqueue(name, 0, 0);
+ if (!slot->wq)
+ goto abort;
+
slot->ctrl = ctrl;
mutex_init(&slot->lock);
INIT_DELAYED_WORK(&slot->work, pciehp_queue_pushbutton_work);
ctrl->slot = slot;
return 0;
+abort:
+ kfree(slot);
+ return -ENOMEM;
}

static void pcie_cleanup_slot(struct controller *ctrl)
{
struct slot *slot = ctrl->slot;
cancel_delayed_work(&slot->work);
- flush_workqueue(pciehp_wq);
+ destroy_workqueue(slot->wq);
kfree(slot);
}




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