Date:   Tue, 12 Dec 2017 17:31:51 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        liudongdong3@...wei.com, linux-arm-kernel@...ts.infradead.org,
        arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH][resend] pciehp: fix a race between pciehp and
 removing operations by sysfs

On Tue, Dec 12, 2017 at 07:30:31PM +0800, Xiongfeng Wang wrote:
> This patch seems to introduce another issue. pciehp_power_thread() use
> 'container_of' to get the 'slot' according to 'work_struct'.
> If the 'slot' has been freed before that, there will be an issue.

1) This claims to be a resend, but I don't see any previous patches
with this subject or from this email address.  Maybe the previous
posting didn't make it to the list because it ran afoul of the
mailing list guidelines at
http://vger.kernel.org/majordomo-info.html#taboo?

2) Please also use the Linux convention of putting your response
*below* the question.

3) Since you say your patch introduces another issue, I'll drop the
patch for now, and you can post a revised version when it's ready.

> On 2017/12/12 16:29, Xiongfeng Wang wrote:
> > 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@...wei.com>
> > ---
> >  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)
> > 
> 
> 
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