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

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Submitter Gu Zheng
Date Feb. 6, 2013, 10:16 a.m.
Message ID <51122D9A.6040002@cn.fujitsu.com>
Download mbox | patch
Permalink /patch/218530/
State Rejected
Headers show

Comments

Gu Zheng - Feb. 6, 2013, 10:16 a.m.
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(-)


@@ -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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Gu Zheng - May 9, 2013, 10:41 a.m.
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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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


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Bjorn Helgaas - May 9, 2013, 4:53 p.m.
On Thu, May 9, 2013 at 3:41 AM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
> 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! :)

No problem, thanks for reminding me about this.  I hadn't actually
forgotten about this patch, but it does seem like it's tangled up with
the whole pci_bus and pci_dev reference counting situation, so I was
hoping that if we could figure out a clean resolution to that, it
would make it more obvious what to do here.

Bjorn

> 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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>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
>
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Bjorn Helgaas - July 31, 2013, 11:08 p.m.
On Thu, May 9, 2013 at 10:53 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Thu, May 9, 2013 at 3:41 AM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
>> 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! :)
>
> No problem, thanks for reminding me about this.  I hadn't actually
> forgotten about this patch, but it does seem like it's tangled up with
> the whole pci_bus and pci_dev reference counting situation, so I was
> hoping that if we could figure out a clean resolution to that, it
> would make it more obvious what to do here.

Gu, can you open a bugzilla for this (or include a URL here if a
bugzilla already exists)?  Please include a recipe showing how to
reproduce the problem and attach a transcript, e.g., a complete dmesg
from which the portion below was extracted.  Thanks!

Bjorn

>> 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
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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Gu Zheng - Aug. 1, 2013, 5:45 a.m.
On 08/01/2013 07:08 AM, Bjorn Helgaas wrote:

> On Thu, May 9, 2013 at 10:53 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
>> On Thu, May 9, 2013 at 3:41 AM, Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
>>> 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! :)
>>
>> No problem, thanks for reminding me about this.  I hadn't actually
>> forgotten about this patch, but it does seem like it's tangled up with
>> the whole pci_bus and pci_dev reference counting situation, so I was
>> hoping that if we could figure out a clean resolution to that, it
>> would make it more obvious what to do here.
> 
> Gu, can you open a bugzilla for this (or include a URL here if a
> bugzilla already exists)?  Please include a recipe showing how to
> reproduce the problem and attach a transcript, e.g., a complete dmesg
> from which the portion below was extracted.  Thanks!

Hi Bjorn,
	I filed a bugzilla about this issue, and attached some useful infos,
hope this can help you.:)

bugzilla url:https://bugzilla.kernel.org/show_bug.cgi?id=60672
 
Regards,
Gu

> 
> Bjorn
> 
>>> 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
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>
>>>
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>>> the body of a message to majordomo@vger.kernel.org
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> 


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Patch

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;
 }