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Date:   Thu, 1 Aug 2019 19:36:18 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pciehp: fix a race between pciehp and removing
 operations by sysfs
Message-ID: <20190802003618.GJ151852@google.com>
References: <1519648875-38196-1-git-send-email-wangxiongfeng2@huawei.com>
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On Mon, Feb 26, 2018 at 08:41:15PM +0800, Xiongfeng Wang wrote:
> From: Xiongfeng Wang <xiongfeng.wang@linaro.com>
> 
> When I run a stress test about pcie hotplug and removing operations by
> sysfs, I got a hange task, and the following call trace is printed.

It's been so long that I'm embarrassed to even respond to this, but
this patch doesn't apply cleanly to v5.3-rc1.  If this is still a
problem, would you mind refreshing it and reposting it?  Thanks.

>  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
> 
> There is a race condition between these two kinds of operations.
> 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
> call pciehp_unconfigure_device(), which will try to get a global mutex
> lock 'pci_rescan_remove_lock'.
> 
> 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 but failed, so it will just
> wait. 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 occurs.
> 
> So this two kinds of operation, removing through attention buttion and
> removing through /sys/devices/pci***/remove, should not be excuted at the
> same time. This patch add a global variable to mark that one of these
> operations is under processing. When this variable is set,  if another
> operation is requested, it will be rejected.
> 
> At first, I want to add a flag for each pci slot to record whether a
> removing operation is under processing. When a bridge is being removed,
> the flags of all the slots below the bridge need to be checked. But it
> is hard for us to guarantee the atomic access. So I just use a global
> flag.
> 
> Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
> ---
>  drivers/pci/hotplug/pciehp_ctrl.c |  7 +++++++
>  drivers/pci/hotplug/pciehp_hpc.c  | 12 +++++++++++-
>  drivers/pci/pci-sysfs.c           | 11 +++++++++--
>  drivers/pci/remove.c              |  6 ++++++
>  include/linux/pci.h               |  3 +++
>  5 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index c684faa..e6fc5d7 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -30,6 +30,7 @@ void pciehp_queue_interrupt_event(struct slot *p_slot, u32 event_type)
>  	info = kmalloc(sizeof(*info), GFP_ATOMIC);
>  	if (!info) {
>  		ctrl_err(p_slot->ctrl, "dropped event %d (ENOMEM)\n", event_type);
> +		slot_being_removed_rescanned = 0;
>  		return;
>  	}
>  
> @@ -174,6 +175,7 @@ static void pciehp_power_thread(struct work_struct *work)
>  		mutex_lock(&p_slot->lock);
>  		p_slot->state = STATIC_STATE;
>  		mutex_unlock(&p_slot->lock);
> +		slot_being_removed_rescanned = 0;
>  		break;
>  	case ENABLE_REQ:
>  		mutex_lock(&p_slot->hotplug_lock);
> @@ -184,6 +186,7 @@ static void pciehp_power_thread(struct work_struct *work)
>  		mutex_lock(&p_slot->lock);
>  		p_slot->state = STATIC_STATE;
>  		mutex_unlock(&p_slot->lock);
> +		slot_being_removed_rescanned = 0;
>  		break;
>  	default:
>  		break;
> @@ -202,6 +205,7 @@ static void pciehp_queue_power_work(struct slot *p_slot, int req)
>  	if (!info) {
>  		ctrl_err(p_slot->ctrl, "no memory to queue %s request\n",
>  			 (req == ENABLE_REQ) ? "poweron" : "poweroff");
> +		slot_being_removed_rescanned = 0;
>  		return;
>  	}
>  	info->p_slot = p_slot;
> @@ -270,6 +274,7 @@ static void handle_button_press_event(struct slot *p_slot)
>  		ctrl_info(ctrl, "Slot(%s): Action canceled due to button press\n",
>  			  slot_name(p_slot));
>  		p_slot->state = STATIC_STATE;
> +		slot_being_removed_rescanned = 0;
>  		break;
>  	case POWEROFF_STATE:
>  	case POWERON_STATE:
> @@ -280,10 +285,12 @@ static void handle_button_press_event(struct slot *p_slot)
>  		 */
>  		ctrl_info(ctrl, "Slot(%s): Button ignored\n",
>  			  slot_name(p_slot));
> +		slot_being_removed_rescanned = 0;
>  		break;
>  	default:
>  		ctrl_err(ctrl, "Slot(%s): Ignoring invalid state %#x\n",
>  			 slot_name(p_slot), p_slot->state);
> +		slot_being_removed_rescanned = 0;
>  		break;
>  	}
>  }
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 18a42f8..5ef5387 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -608,7 +608,17 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
>  	if (events & PCI_EXP_SLTSTA_ABP) {
>  		ctrl_info(ctrl, "Slot(%s): Attention button pressed\n",
>  			  slot_name(slot));
> -		pciehp_queue_interrupt_event(slot, INT_BUTTON_PRESS);
> +
> +		if (!test_and_set_bit(0, &slot_being_removed_rescanned))
> +			pciehp_queue_interrupt_event(slot, INT_BUTTON_PRESS);
> +		else {
> +			if (slot->state == BLINKINGOFF_STATE || slot->state == BLINKINGON_STATE)
> +				pciehp_queue_interrupt_event(slot, INT_BUTTON_PRESS);
> +			else
> +				ctrl_info(ctrl, "Slot(%s): Slot operation failed because a remove or"
> +					" rescan operation is under processing, please try later!\n",
> +					slot_name(slot));
> +		}
>  	}
>  
>  	/*
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index eb6bee8..9fd1699 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -499,8 +499,15 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
>  	if (kstrtoul(buf, 0, &val) < 0)
>  		return -EINVAL;
>  
> -	if (val && device_remove_file_self(dev, attr))
> -		pci_stop_and_remove_bus_device_locked(to_pci_dev(dev));
> +	if (val && device_remove_file_self(dev, attr)) {
> +		if (!test_and_set_bit(0, &slot_being_removed_rescanned)) {
> +			pci_stop_and_remove_bus_device_locked(to_pci_dev(dev));
> +			slot_being_removed_rescanned = 0;
> +		} else {
> +			pr_info("Slot is being removed or rescanned, please try later!\n");
> +			return -EPERM;
> +		}
> +	}
>  	return count;
>  }
>  static struct device_attribute dev_remove_attr = __ATTR(remove,
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 6f072ea..6d36d53 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -4,6 +4,12 @@
>  #include <linux/pci-aspm.h>
>  #include "pci.h"
>  
> +/*
> + * When a slot is being hotplug through Attention Button or being
> + * removed/rescanned through sysfs, this flag is set.
> + */
> +unsigned long slot_being_removed_rescanned;
> +
>  static void pci_free_resources(struct pci_dev *dev)
>  {
>  	int i;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 024a1be..e1711ce 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -846,6 +846,9 @@ enum pcie_bus_config_types {
>  /* Do NOT directly access these two variables, unless you are arch-specific PCI
>   * code, or PCI core code. */
>  extern struct list_head pci_root_buses;	/* List of all known PCI buses */
> +
> +extern unsigned long slot_being_removed_rescanned;
> +
>  /* Some device drivers need know if PCI is initiated */
>  int no_pci_devices(void);
>  
> -- 
> 1.7.12.4
>