[RFC PATCH][resend] pciehp: fix a race between pciehp and removing operations by sysfs

[Xiongfeng Wang]

When the Attention button on a PCIE slot is pressed, 5 seconds later,
pciehp_power_thread() will be scheduled on slot->wq. This function will
get a global mutex lock 'pci_rescan_remove_lock' in
pciehp_unconfigure_device().

At the same time, we remove the pcie port by sysfs, which results in
pci_stop_and_remove_bus_device_locked() called. This function will get
the global mutex lock 'pci_rescan_remove_lock', and then release the
struct 'ctrl', which will wait until the work_struct on slot->wq is
finished.

If pci_stop_and_remove_bus_device_locked() got the mutex lock, and
before it drains workqueue slot->wq, pciehp_power_thread() is scheduled
on slot->wq and tries to get the mutex lock. Then
pci_stop_and_remove_bus_device_locked() tries to drain workqueue
slot->wq and wait until work struct 'pciehp_power_thread()' is finished.
Then a hung_task happens.

This patch solve this problem by schedule 'pciehp_power_thread()' on a
system workqueue instead of slot->wq.

The Call Trace we got is as following.

 INFO: task kworker/0:2:4413 blocked for more than 120 seconds.
       Tainted: P        W  O    4.12.0-rc1 #1
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 kworker/0:2     D    0  4413      2 0x00000000
 Workqueue: pciehp-0 pciehp_power_thread
 Call trace:
 [<ffff0000080861d4>] __switch_to+0x94/0xa8
 [<ffff000008bea9c0>] __schedule+0x1b0/0x708
 [<ffff000008beaf58>] schedule+0x40/0xa4
 [<ffff000008beb33c>] schedule_preempt_disabled+0x28/0x40
 [<ffff000008bec1dc>] __mutex_lock.isra.8+0x148/0x50c
 [<ffff000008bec5c4>] __mutex_lock_slowpath+0x24/0x30
 [<ffff000008bec618>] mutex_lock+0x48/0x54
 [<ffff0000084d8188>] pci_lock_rescan_remove+0x20/0x28
 [<ffff0000084f87c0>] pciehp_unconfigure_device+0x54/0x1cc
 [<ffff0000084f8260>] pciehp_disable_slot+0x4c/0xbc
 [<ffff0000084f8370>] pciehp_power_thread+0xa0/0xb8
 [<ffff0000080e9ce8>] process_one_work+0x13c/0x3f8
 [<ffff0000080ea004>] worker_thread+0x60/0x3e4
 [<ffff0000080f0814>] kthread+0x10c/0x138
 [<ffff0000080836c0>] ret_from_fork+0x10/0x50
 INFO: task bash:31732 blocked for more than 120 seconds.
       Tainted: P        W  O    4.12.0-rc1 #1
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 bash            D    0 31732      1 0x00000009
 Call trace:
 [<ffff0000080861d4>] __switch_to+0x94/0xa8
 [<ffff000008bea9c0>] __schedule+0x1b0/0x708
 [<ffff000008beaf58>] schedule+0x40/0xa4
 [<ffff000008bee7b4>] schedule_timeout+0x1a0/0x340
 [<ffff000008bebb88>] wait_for_common+0x108/0x1bc
 [<ffff000008bebc64>] wait_for_completion+0x28/0x34
 [<ffff0000080e7594>] flush_workqueue+0x130/0x488
 [<ffff0000080e79b0>] drain_workqueue+0xc4/0x164
 [<ffff0000080ec3cc>] destroy_workqueue+0x28/0x1f4
 [<ffff0000084fa094>] pciehp_release_ctrl+0x34/0xe0
 [<ffff0000084f75b0>] pciehp_remove+0x30/0x3c
 [<ffff0000084f24d8>] pcie_port_remove_service+0x3c/0x54
 [<ffff00000876b1e4>] device_release_driver_internal+0x150/0x1d0
 [<ffff00000876b28c>] device_release_driver+0x28/0x34
 [<ffff00000876a018>] bus_remove_device+0xe0/0x11c
 [<ffff000008766348>] device_del+0x200/0x304
 [<ffff00000876646c>] device_unregister+0x20/0x38
 [<ffff0000084f2560>] remove_iter+0x44/0x54
 [<ffff000008765230>] device_for_each_child+0x4c/0x90
 [<ffff0000084f2c98>] pcie_port_device_remove+0x2c/0x48
 [<ffff0000084f2f48>] pcie_portdrv_remove+0x60/0x6c
 [<ffff0000084e3de4>] pci_device_remove+0x48/0x110
 [<ffff00000876b1e4>] device_release_driver_internal+0x150/0x1d0
 [<ffff00000876b28c>] device_release_driver+0x28/0x34
 [<ffff0000084db028>] pci_stop_bus_device+0x9c/0xac
 [<ffff0000084db190>] pci_stop_and_remove_bus_device_locked+0x24/0x3c
 [<ffff0000084e5eb0>] remove_store+0x74/0x80
 [<ffff000008764680>] dev_attr_store+0x44/0x5c
 [<ffff0000082e7e1c>] sysfs_kf_write+0x5c/0x74
 [<ffff0000082e7014>] kernfs_fop_write+0xcc/0x1dc
 [<ffff0000082602e0>] __vfs_write+0x48/0x13c
 [<ffff00000826174c>] vfs_write+0xa8/0x198
 [<ffff000008262ce8>] SyS_write+0x54/0xb0
 [<ffff000008083730>] el0_svc_naked+0x24/0x28

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
---
 drivers/pci/hotplug/pciehp_ctrl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index 83f3d4a..9d39d85 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -221,7 +221,7 @@ static void pciehp_queue_power_work(struct slot *p_slot, int req)
 	info->p_slot = p_slot;
 	INIT_WORK(&info->work, pciehp_power_thread);
 	info->req = req;
-	queue_work(p_slot->wq, &info->work);
+	schedule_work(&info->work);
 }
 
 void pciehp_queue_pushbutton_work(struct work_struct *work)
-- 
1.7.12.4