Re: pci-sysfs: queue sysfs rescan routine into workqueue to avoid potential deadlock situation

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Hi Bjorn,
	Very sorry to disturb you. This patch was sent a long time ago, but we have not get
any feedback until now.
It is used to fix a potential deadlock situation when doing pci-hotplug via pci-sysfs.
In the first version we sent:
https://patchwork.kernel.org/patch/1912351/
replaced mutex_lock with mutex_trylock to avoid potential deadlock situation, but you suggested
that using a workqueue to queue these routines seems a good way to avoid the deadlock situation,
and this patch was followed your suggestion, can your split a while to review it? Or is there any
better way to fix this issue? Any comments is welcome! :)

Best regards,
Gu

On 02/06/2013 06:16 PM, Gu Zheng wrote:

> There is a potential deadlock situation when we manipulate the pci-sysfs user
> interfaces from different bus hierarchy simultaneously, described as following:
> 
> path1: sysfs remove device:             | path2: sysfs rescan device:
> sysfs_schedule_callback_work()          | sysfs_write_file()
>   remove_callback()                     |   flush_write_buffer()
> *1* mutex_lock(&pci_remove_rescan_mutex)|*2*  sysfs_get_active(attr_sd)
>       ...                               |     dev_attr_store()
>         device_remove_file()            |       dev_rescan_store()
>           ...                           |*4*
> mutex_lock(&pci_remove_rescan_mutex)
> *3*       sysfs_deactivate(sd)          |     ...
>             wait_for_completion()       |*5*  sysfs_put_active(attr_sd)
> *6* mutex_unlock(&pci_remove_rescan_mutex)
> 
> If path1 first holds the pci_remove_rescan_mutex at *1*, then another path
> called path2 actived and runs to *2* before path1 runs to *3*, we now runs
> to a deadlock situation:
> Path1 holds the mutex waiting path2 to decrease sysfs_dirent's s_active
> counter at *5*, but path2 is blocked at *4* when trying to get the
> pci_remove_rescan_mutex. The mutex won't be put by path1 until it reach
> *6*, but it's now blocked at *3*.
> 
> Under the suggestion of Bjorn, and base on Yinghai Lu's patch:
> http://git.kernel.org/?p=linux/kernel/git/yinghai/linux-yinghai.git;a=commitdiff;h=277df390baeab7ba6aa136356b677a096c890c0c
> 
> The circumvent approach is queuing the sysfs rescan routine into workqueue just
> like removal to avoid manipulating(remove/scan) the pci-tree at the same time.
> 
> 
> *dmesg ifno*:
> (snip)
> 1000e 0000:1c:00.0: eth9: Intel(R) PRO/1000 Network Connection
> sd 13:2:0:0: [sdb] Attached SCSI disk
> e1000e 0000:1c:00.0: eth9: MAC: 0, PHY: 4, PBA No: D50228-005
> e1000e 0000:1c:00.1: Disabling ASPM  L1
> e1000e 0000:1c:00.1: Interrupt Throttling Rate (ints/sec) set to dynamic
> conservative mode
> e1000e 0000:1c:00.1: irq 143 for MSI/MSI-X
> e1000e 0000:1c:00.1: eth10: (PCI Express:2.5GT/s:Width x4) 00:15:17:cd:96:bf
> e1000e 0000:1c:00.1: eth10: Intel(R) PRO/1000 Network Connection
> e1000e 0000:1c:00.1: eth10: MAC: 0, PHY: 4, PBA No: D50228-005
> INFO: task bash:62982 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> bash            D 0000000000000000     0 62982  62978 0x00000080
>  ffff88038b277db8 0000000000000082 ffff88038b277fd8 0000000000013940
>  ffff88038b276010 0000000000013940 0000000000013940 0000000000013940
>  ffff88038b277fd8 0000000000013940 ffff880377449e30 ffff8806e822c670
> Call Trace:
>  [<ffffffff8151ba79>] schedule+0x29/0x70
>  [<ffffffff8151bd6e>] schedule_preempt_disabled+0xe/0x10
>  [<ffffffff8151a4e3>] __mutex_lock_slowpath+0xd3/0x150
>  [<ffffffff8151a3eb>] mutex_lock+0x2b/0x50
>  [<ffffffff812821dc>] dev_rescan_store+0x5c/0x80
>  [<ffffffff81341800>] dev_attr_store+0x20/0x30
>  [<ffffffff811e3eef>] sysfs_write_file+0xef/0x170
>  [<ffffffff81173d08>] vfs_write+0xc8/0x190
>  [<ffffffff81173ed1>] sys_write+0x51/0x90
>  [<ffffffff81524b29>] system_call_fastpath+0x16/0x1b
> INFO: task bash:64141 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> bash            D ffffffff81610460     0 64141  64136 0x00000080
>  ffff8803540e9db8 0000000000000086 ffff8803540e9fd8 0000000000013940
>  ffff8803540e8010 0000000000013940 0000000000013940 0000000000013940
>  ffff8803540e9fd8 0000000000013940 ffff8807db338a10 ffff8806f09abc60
> Call Trace:
>  [<ffffffff8151ba79>] schedule+0x29/0x70
>  [<ffffffff8151bd6e>] schedule_preempt_disabled+0xe/0x10
>  [<ffffffff8151a4e3>] __mutex_lock_slowpath+0xd3/0x150
>  [<ffffffff8151a3eb>] mutex_lock+0x2b/0x50
>  [<ffffffff812821dc>] dev_rescan_store+0x5c/0x80
>  [<ffffffff81341800>] dev_attr_store+0x20/0x30
>  [<ffffffff811e3eef>] sysfs_write_file+0xef/0x170
>  [<ffffffff81173d08>] vfs_write+0xc8/0x190
>  [<ffffffff81173ed1>] sys_write+0x51/0x90
>  [<ffffffff81524b29>] system_call_fastpath+0x16/0x1b
> INFO: task kworker/u:3:64451 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> kworker/u:3     D ffffffff81610460     0 64451      2 0x00000080
>  ffff8807d51b7a30 0000000000000046 ffff8807d51b7fd8 0000000000013940
>  ffff8807d51b6010 0000000000013940 0000000000013940 0000000000013940
>  ffff8807d51b7fd8 0000000000013940 ffff8807db339420 ffff88037744b250
> Call Trace:
>  [<ffffffff8151ba79>] schedule+0x29/0x70
>  [<ffffffff81519ded>] schedule_timeout+0x19d/0x220
>  [<ffffffff81165f92>] ? __slab_free+0x1f2/0x2f0
>  [<ffffffff8151b8fe>] wait_for_common+0x11e/0x190
>  [<ffffffff8108a6e0>] ? try_to_wake_up+0x2c0/0x2c0
>  [<ffffffff8151ba4d>] wait_for_completion+0x1d/0x20
>  [<ffffffff811e53e8>] sysfs_addrm_finish+0xb8/0xd0
>  [<ffffffff811e4320>] ? sysfs_schedule_callback+0x1e0/0x1e0
>  [<ffffffff811e33f0>] sysfs_hash_and_remove+0x60/0xb0
>  [<ffffffff811e43c9>] sysfs_remove_file+0x39/0x50
>  [<ffffffff81342cb7>] device_remove_file+0x17/0x20
>  [<ffffffff8134505c>] bus_remove_device+0xdc/0x180
>  [<ffffffff81342eb0>] device_del+0x120/0x1d0
>  [<ffffffff81342f82>] device_unregister+0x22/0x60
>  [<ffffffff8127ade4>] pci_stop_bus_device+0x94/0xa0
>  [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0
>  [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0
>  [<ffffffff8127ad90>] pci_stop_bus_device+0x40/0xa0
>  [<ffffffff8127af66>] pci_stop_and_remove_bus_device+0x16/0x30
>  [<ffffffff81282359>] remove_callback+0x29/0x40
>  [<ffffffff811e4344>] sysfs_schedule_callback_work+0x24/0x70
>  [<ffffffff81070009>] process_one_work+0x179/0x4b0
>  [<ffffffff8107210e>] worker_thread+0x12e/0x330
>  [<ffffffff81071fe0>] ? manage_workers+0x110/0x110
>  [<ffffffff8107705e>] kthread+0x9e/0xb0
>  [<ffffffff81525bc4>] kernel_thread_helper+0x4/0x10
>  [<ffffffff81076fc0>] ? kthread_freezable_should_stop+0x70/0x70
>  [<ffffffff81525bc0>] ? gs_change+0x13/0x13
> 
> 
> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> Signed-off-by: Lin Feng <linfeng@cn.fujitsu.com>
> ---
>  drivers/pci/pci-sysfs.c |   92 +++++++++++++++++++++++++++++++++--------------
>  1 files changed, 65 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 9c6e9bb..e66b498 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -285,21 +285,34 @@ msi_bus_store(struct device *dev, struct device_attribute
> *attr,
>  }
> 
>  static DEFINE_MUTEX(pci_remove_rescan_mutex);
> +
> +static void bus_rescan_callback(struct device *dev)
> +{
> +	struct pci_bus *b = NULL;
> +
> +	mutex_lock(&pci_remove_rescan_mutex);
> +	while ((b = pci_find_next_bus(b)) != NULL)
> +		pci_rescan_bus(b);
> +	mutex_unlock(&pci_remove_rescan_mutex);
> +}
> +
>  static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf,
>  				size_t count)
>  {
> +	int err;
>  	unsigned long val;
> -	struct pci_bus *b = NULL;
> +	struct device *dev = bus->dev_root;
> 
>  	if (strict_strtoul(buf, 0, &val) < 0)
>  		return -EINVAL;
> 
> -	if (val) {
> -		mutex_lock(&pci_remove_rescan_mutex);
> -		while ((b = pci_find_next_bus(b)) != NULL)
> -			pci_rescan_bus(b);
> -		mutex_unlock(&pci_remove_rescan_mutex);
> -	}
> +	if (!val)
> +		return count;
> +
> +	err = device_schedule_callback(dev, bus_rescan_callback);
> +	if (err)
> +		return err;
> +
>  	return count;
>  }
> 
> @@ -308,21 +321,32 @@ struct bus_attribute pci_bus_attrs[] = {
>  	__ATTR_NULL
>  };
> 
> +static void dev_rescan_callback(struct device *dev)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +
> +	if (pdev->is_added) {
> +		mutex_lock(&pci_remove_rescan_mutex);
> +		pci_rescan_bus(pdev->bus);
> +		mutex_unlock(&pci_remove_rescan_mutex);
> +	}
> +}
> +
>  static ssize_t
>  dev_rescan_store(struct device *dev, struct device_attribute *attr,
>  		 const char *buf, size_t count)
>  {
> +	int err;
>  	unsigned long val;
> -	struct pci_dev *pdev = to_pci_dev(dev);
> 
>  	if (strict_strtoul(buf, 0, &val) < 0)
>  		return -EINVAL;
> 
> -	if (val) {
> -		mutex_lock(&pci_remove_rescan_mutex);
> -		pci_rescan_bus(pdev->bus);
> -		mutex_unlock(&pci_remove_rescan_mutex);
> -	}
> +	if (!val)
> +		return count;
> +	err = device_schedule_callback(dev, dev_rescan_callback);
> +	if (err)
> +		return err;
>  	return count;
>  }
> 
> @@ -339,7 +363,7 @@ static ssize_t
>  remove_store(struct device *dev, struct device_attribute *dummy,
>  	     const char *buf, size_t count)
>  {
> -	int ret = 0;
> +	int err;
>  	unsigned long val;
> 
>  	if (strict_strtoul(buf, 0, &val) < 0)
> @@ -348,31 +372,45 @@ remove_store(struct device *dev, struct device_attribute
> *dummy,
>  	/* An attribute cannot be unregistered by one of its own methods,
>  	 * so we have to use this roundabout approach.
>  	 */
> -	if (val)
> -		ret = device_schedule_callback(dev, remove_callback);
> -	if (ret)
> -		count = ret;
> +	if (!val)
> +		return count;
> +
> +	err = device_schedule_callback(dev, remove_callback);
> +	if (err)
> +		return err;
> +
>  	return count;
>  }
> 
> +static void dev_bus_rescan_callback(struct device *dev)
> +{
> +	struct pci_bus *bus = to_pci_bus(dev);
> +
> +	mutex_lock(&pci_remove_rescan_mutex);
> +	if (!pci_is_root_bus(bus) && list_empty(&bus->devices))
> +		pci_rescan_bus_bridge_resize(bus->self);
> +	else
> +		pci_rescan_bus(bus);
> +	mutex_unlock(&pci_remove_rescan_mutex);
> +}
> +
>  static ssize_t
>  dev_bus_rescan_store(struct device *dev, struct device_attribute *attr,
>  		 const char *buf, size_t count)
>  {
> +	int err;
>  	unsigned long val;
> -	struct pci_bus *bus = to_pci_bus(dev);
> 
>  	if (strict_strtoul(buf, 0, &val) < 0)
>  		return -EINVAL;
> 
> -	if (val) {
> -		mutex_lock(&pci_remove_rescan_mutex);
> -		if (!pci_is_root_bus(bus) && list_empty(&bus->devices))
> -			pci_rescan_bus_bridge_resize(bus->self);
> -		else
> -			pci_rescan_bus(bus);
> -		mutex_unlock(&pci_remove_rescan_mutex);
> -	}
> +	if (!val)
> +		return count;
> +
> +	err = device_schedule_callback(dev, dev_bus_rescan_callback);
> +	if (err)
> +		return err;
> +
>  	return count;
>  }
> 
> -- 1.7.7
> 
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