[PATCH 1/3] scsi: serialize ->rescan against ->remove

[PATCH 1/3] scsi: serialize ->rescan against ->remove

[Christoph Hellwig]

Lock the device embedded in the scsi_device to protect against
concurrent calls to ->remove.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/scsi/scsi_scan.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 983aed1..523faee 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
 
 void scsi_rescan_device(struct device *dev)
 {
-	if (!dev->driver)
-		return;
-
-	if (try_module_get(dev->driver->owner)) {
+	device_lock(dev);
+	if (dev->driver && try_module_get(dev->driver->owner)) {
 		struct scsi_driver *drv = to_scsi_driver(dev->driver);
 
 		if (drv->rescan)
 			drv->rescan(dev);
 		module_put(dev->driver->owner);
 	}
+	device_unlock(dev);
 }
 EXPORT_SYMBOL(scsi_rescan_device);
 
-- 
1.9.1

[PATCH 2/3] sd: don't grab a device references from driver methods

[Christoph Hellwig]

The device model already takes care of races between ->remove and
->shutdown vs its other methods, and we now take care about locking
them out for ->rescan as well.

This is a partial revert of commit 39b7f1 ("[SCSI] sd: Fix refcounting").

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/scsi/sd.c | 55 +++++++++++--------------------------------------------
 1 file changed, 11 insertions(+), 44 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 3995169..1f06274 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -564,10 +564,12 @@ static int sd_major(int major_idx)
 	}
 }
 
-static struct scsi_disk *__scsi_disk_get(struct gendisk *disk)
+static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
 {
 	struct scsi_disk *sdkp = NULL;
 
+	mutex_lock(&sd_ref_mutex);
+
 	if (disk->private_data) {
 		sdkp = scsi_disk(disk);
 		if (scsi_device_get(sdkp->device) == 0)
@@ -575,27 +577,6 @@ static struct scsi_disk *__scsi_disk_get(struct gendisk *disk)
 		else
 			sdkp = NULL;
 	}
-	return sdkp;
-}
-
-static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
-{
-	struct scsi_disk *sdkp;
-
-	mutex_lock(&sd_ref_mutex);
-	sdkp = __scsi_disk_get(disk);
-	mutex_unlock(&sd_ref_mutex);
-	return sdkp;
-}
-
-static struct scsi_disk *scsi_disk_get_from_dev(struct device *dev)
-{
-	struct scsi_disk *sdkp;
-
-	mutex_lock(&sd_ref_mutex);
-	sdkp = dev_get_drvdata(dev);
-	if (sdkp)
-		sdkp = __scsi_disk_get(sdkp->disk);
 	mutex_unlock(&sd_ref_mutex);
 	return sdkp;
 }
@@ -610,8 +591,6 @@ static void scsi_disk_put(struct scsi_disk *sdkp)
 	mutex_unlock(&sd_ref_mutex);
 }
 
-
-
 static unsigned char sd_setup_protect_cmnd(struct scsi_cmnd *scmd,
 					   unsigned int dix, unsigned int dif)
 {
@@ -1525,12 +1504,9 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 
 static void sd_rescan(struct device *dev)
 {
-	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
+	struct scsi_disk *sdkp = dev_get_drvdata(dev);
 
-	if (sdkp) {
-		revalidate_disk(sdkp->disk);
-		scsi_disk_put(sdkp);
-	}
+	revalidate_disk(sdkp->disk);
 }
 
 
@@ -3147,13 +3123,13 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, int start)
  */
 static void sd_shutdown(struct device *dev)
 {
-	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
+	struct scsi_disk *sdkp = dev_get_drvdata(dev);
 
 	if (!sdkp)
 		return;         /* this can happen */
 
 	if (pm_runtime_suspended(dev))
-		goto exit;
+		return;
 
 	if (sdkp->WCE && sdkp->media_present) {
 		sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
@@ -3164,14 +3140,11 @@ static void sd_shutdown(struct device *dev)
 		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
 		sd_start_stop_device(sdkp, 0);
 	}
-
-exit:
-	scsi_disk_put(sdkp);
 }
 
 static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 {
-	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
+	struct scsi_disk *sdkp = dev_get_drvdata(dev);
 	int ret = 0;
 
 	if (!sdkp)
@@ -3197,7 +3170,6 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 	}
 
 done:
-	scsi_disk_put(sdkp);
 	return ret;
 }
 
@@ -3213,18 +3185,13 @@ static int sd_suspend_runtime(struct device *dev)
 
 static int sd_resume(struct device *dev)
 {
-	struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
-	int ret = 0;
+	struct scsi_disk *sdkp = dev_get_drvdata(dev);
 
 	if (!sdkp->device->manage_start_stop)
-		goto done;
+		return 0;
 
 	sd_printk(KERN_NOTICE, sdkp, "Starting disk\n");
-	ret = sd_start_stop_device(sdkp, 1);
-
-done:
-	scsi_disk_put(sdkp);
-	return ret;
+	return sd_start_stop_device(sdkp, 1);
 }
 
 /**
-- 
1.9.1

[PATCH 3/3] scsi: proper state checking and module refcount handling in scsi_device_get

[Christoph Hellwig]

This effectively reverts commits 85b6c7 ("[SCSI] sd: fix cache flushing on
module removal (and individual device removal)" and dc4515ea ("scsi: always
increment reference count").

We now never call scsi_device_get from the shutdown path, and the fact
that we started grabbing reference there in commit 85b6c7 turned out
turned out to create more problems than it solves, and required
workarounds for workarounds for workarounds. Move back to properly checking
the device state and carefully handle module refcounting.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/scsi/scsi.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 9b38299..95f0293 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -982,15 +982,18 @@ EXPORT_SYMBOL(scsi_report_opcode);
  */
 int scsi_device_get(struct scsi_device *sdev)
 {
-	if (sdev->sdev_state == SDEV_DEL)
-		return -ENXIO;
+	if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
+		goto fail;
 	if (!get_device(&sdev->sdev_gendev))
-		return -ENXIO;
-	/* We can fail try_module_get if we're doing SCSI operations
-	 * from module exit (like cache flush) */
-	__module_get(sdev->host->hostt->module);
-
+		goto fail;
+	if (!try_module_get(sdev->host->hostt->module))
+		goto fail_put_device;
 	return 0;
+
+fail_put_device:
+	put_device(&sdev->sdev_gendev);
+fail:
+	return -ENXIO;
 }
 EXPORT_SYMBOL(scsi_device_get);
 
-- 
1.9.1

Re: [PATCH 3/3] scsi: proper state checking and module refcount handling in scsi_device_get

[James Bottomley]

On Thu, 2015-01-29 at 00:00 +0100, Christoph Hellwig wrote:
> This effectively reverts commits 85b6c7 ("[SCSI] sd: fix cache flushing on
> module removal (and individual device removal)" and dc4515ea ("scsi: always
> increment reference count").
> 
> We now never call scsi_device_get from the shutdown path, and the fact
> that we started grabbing reference there in commit 85b6c7 turned out
> turned out to create more problems than it solves, and required
> workarounds for workarounds for workarounds. Move back to properly checking
> the device state and carefully handle module refcounting.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/scsi/scsi.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 9b38299..95f0293 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -982,15 +982,18 @@ EXPORT_SYMBOL(scsi_report_opcode);
>   */
>  int scsi_device_get(struct scsi_device *sdev)
>  {
> -	if (sdev->sdev_state == SDEV_DEL)
> -		return -ENXIO;
> +	if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
> +		goto fail;
>  	if (!get_device(&sdev->sdev_gendev))
> -		return -ENXIO;
> -	/* We can fail try_module_get if we're doing SCSI operations
> -	 * from module exit (like cache flush) */
> -	__module_get(sdev->host->hostt->module);
> -
> +		goto fail;
> +	if (!try_module_get(sdev->host->hostt->module))
> +		goto fail_put_device;
>  	return 0;
> +
> +fail_put_device:
> +	put_device(&sdev->sdev_gendev);
> +fail:
> +	return -ENXIO;
>  }
>  EXPORT_SYMBOL(scsi_device_get);

If we can get away with this, I'm all for this approach.  However, you
need to document in a comment or above the function that it may not be
called in module exit functions and why.

Other than the comment issue, the series looks good,

Thanks,

James

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Alan Stern]

On Thu, 29 Jan 2015, Christoph Hellwig wrote:

> Lock the device embedded in the scsi_device to protect against
> concurrent calls to ->remove.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/scsi/scsi_scan.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 983aed1..523faee 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
>  
>  void scsi_rescan_device(struct device *dev)
>  {
> -	if (!dev->driver)
> -		return;
> -
> -	if (try_module_get(dev->driver->owner)) {
> +	device_lock(dev);
> +	if (dev->driver && try_module_get(dev->driver->owner)) {
>  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
>  
>  		if (drv->rescan)
>  			drv->rescan(dev);
>  		module_put(dev->driver->owner);
>  	}
> +	device_unlock(dev);
>  }
>  EXPORT_SYMBOL(scsi_rescan_device);

Acked-by: Alan Stern <stern@rowland.harvard.edu>

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 29/01/2015 00:00, Christoph Hellwig wrote:
> Lock the device embedded in the scsi_device to protect against
> concurrent calls to ->remove.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I wonder if this makes this problem: https://lkml.org/lkml/2015/1/5/9 go
away.

Paolo

> ---
>  drivers/scsi/scsi_scan.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 983aed1..523faee 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
>  
>  void scsi_rescan_device(struct device *dev)
>  {
> -	if (!dev->driver)
> -		return;
> -
> -	if (try_module_get(dev->driver->owner)) {
> +	device_lock(dev);
> +	if (dev->driver && try_module_get(dev->driver->owner)) {
>  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
>  
>  		if (drv->rescan)
>  			drv->rescan(dev);
>  		module_put(dev->driver->owner);
>  	}
> +	device_unlock(dev);
>  }
>  EXPORT_SYMBOL(scsi_rescan_device);
>  
> 

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Fam Zheng]

On Fri, 01/30 00:11, Paolo Bonzini wrote:
> 
> 
> On 29/01/2015 00:00, Christoph Hellwig wrote:
> > Lock the device embedded in the scsi_device to protect against
> > concurrent calls to ->remove.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> I wonder if this makes this problem: https://lkml.org/lkml/2015/1/5/9 go
> away.

A quick test says yes.

Fam

> 
> Paolo
> 
> > ---
> >  drivers/scsi/scsi_scan.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> > index 983aed1..523faee 100644
> > --- a/drivers/scsi/scsi_scan.c
> > +++ b/drivers/scsi/scsi_scan.c
> > @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
> >  
> >  void scsi_rescan_device(struct device *dev)
> >  {
> > -	if (!dev->driver)
> > -		return;
> > -
> > -	if (try_module_get(dev->driver->owner)) {
> > +	device_lock(dev);
> > +	if (dev->driver && try_module_get(dev->driver->owner)) {
> >  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
> >  
> >  		if (drv->rescan)
> >  			drv->rescan(dev);
> >  		module_put(dev->driver->owner);
> >  	}
> > +	device_unlock(dev);
> >  }
> >  EXPORT_SYMBOL(scsi_rescan_device);
> >  
> > 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
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Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 30/01/2015 02:08, Fam Zheng wrote:
> On Fri, 01/30 00:11, Paolo Bonzini wrote:
>>
>>
>> On 29/01/2015 00:00, Christoph Hellwig wrote:
>>> Lock the device embedded in the scsi_device to protect against
>>> concurrent calls to ->remove.
>>>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>
>> I wonder if this makes this problem: https://lkml.org/lkml/2015/1/5/9 go
>> away.
> 
> A quick test says yes.

Great, we might want to revert that patch in 3.21.

Paolo

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Christoph Hellwig]

On Fri, Jan 30, 2015 at 10:46:17AM +0100, Paolo Bonzini wrote:
> Great, we might want to revert that patch in 3.21.

Is that fix in any tree yet?  Seems like I missed it for the scsi
tree at least.  So unless you want it for 3.19/stable we might as well
ust skip that patch.

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 02/02/2015 13:59, Christoph Hellwig wrote:
> On Fri, Jan 30, 2015 at 10:46:17AM +0100, Paolo Bonzini wrote:
>> > Great, we might want to revert that patch in 3.21.
> Is that fix in any tree yet?  Seems like I missed it for the scsi
> tree at least.  So unless you want it for 3.19/stable we might as well
> ust skip that patch.

Yes, I agree.

Paolo

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 05/03/2015 14:37, Paolo Bonzini wrote:
> 
> 
> On 05/03/2015 14:33, Christoph Hellwig wrote:
>> Any chance to get reviews for this series?  Also we should at least
>> expedite this first patch into 4.0-rc as it fixes scanning races
>> in virtio_scsi.
> 
> I reviewed 1 and 3, but I'm not really qualified for patch 2.

Christoph,

any news about these patches?

Thanks,

Paolo

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Hannes Reinecke]

On 02/02/2015 08:01 AM, Christoph Hellwig wrote:
> Lock the device embedded in the scsi_device to protect against
> concurrent calls to ->remove.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 05/03/2015 14:33, Christoph Hellwig wrote:
> Any chance to get reviews for this series?  Also we should at least
> expedite this first patch into 4.0-rc as it fixes scanning races
> in virtio_scsi.

I reviewed 1 and 3, but I'm not really qualified for patch 2.

Paolo

> On Mon, Feb 02, 2015 at 02:01:24PM +0100, Christoph Hellwig wrote:
>> Lock the device embedded in the scsi_device to protect against
>> concurrent calls to ->remove.
>>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> Acked-by: Alan Stern <stern@rowland.harvard.edu>
>> ---
>>  drivers/scsi/scsi_scan.c | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
>> index 983aed1..523faee 100644
>> --- a/drivers/scsi/scsi_scan.c
>> +++ b/drivers/scsi/scsi_scan.c
>> @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
>>  
>>  void scsi_rescan_device(struct device *dev)
>>  {
>> -	if (!dev->driver)
>> -		return;
>> -
>> -	if (try_module_get(dev->driver->owner)) {
>> +	device_lock(dev);
>> +	if (dev->driver && try_module_get(dev->driver->owner)) {
>>  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
>>  
>>  		if (drv->rescan)
>>  			drv->rescan(dev);
>>  		module_put(dev->driver->owner);
>>  	}
>> +	device_unlock(dev);
>>  }
>>  EXPORT_SYMBOL(scsi_rescan_device);
>>  
>> -- 
>> 1.9.1
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> ---end quoted text---
> --
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Paolo Bonzini]

On 02/02/2015 14:01, Christoph Hellwig wrote:
> Lock the device embedded in the scsi_device to protect against
> concurrent calls to ->remove.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>
> ---
>  drivers/scsi/scsi_scan.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 983aed1..523faee 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
>  
>  void scsi_rescan_device(struct device *dev)
>  {
> -	if (!dev->driver)
> -		return;
> -
> -	if (try_module_get(dev->driver->owner)) {
> +	device_lock(dev);
> +	if (dev->driver && try_module_get(dev->driver->owner)) {
>  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
>  
>  		if (drv->rescan)
>  			drv->rescan(dev);
>  		module_put(dev->driver->owner);
>  	}
> +	device_unlock(dev);
>  }
>  EXPORT_SYMBOL(scsi_rescan_device);
>  
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Re: [PATCH 1/3] scsi: serialize ->rescan against ->remove

[Christoph Hellwig]

Any chance to get reviews for this series?  Also we should at least
expedite this first patch into 4.0-rc as it fixes scanning races
in virtio_scsi.

On Mon, Feb 02, 2015 at 02:01:24PM +0100, Christoph Hellwig wrote:
> Lock the device embedded in the scsi_device to protect against
> concurrent calls to ->remove.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>
> ---
>  drivers/scsi/scsi_scan.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 983aed1..523faee 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
>  
>  void scsi_rescan_device(struct device *dev)
>  {
> -	if (!dev->driver)
> -		return;
> -
> -	if (try_module_get(dev->driver->owner)) {
> +	device_lock(dev);
> +	if (dev->driver && try_module_get(dev->driver->owner)) {
>  		struct scsi_driver *drv = to_scsi_driver(dev->driver);
>  
>  		if (drv->rescan)
>  			drv->rescan(dev);
>  		module_put(dev->driver->owner);
>  	}
> +	device_unlock(dev);
>  }
>  EXPORT_SYMBOL(scsi_rescan_device);
>  
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
---end quoted text---

[PATCH 1/3] scsi: serialize ->rescan against ->remove

[Christoph Hellwig]

Lock the device embedded in the scsi_device to protect against
concurrent calls to ->remove.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
---
 drivers/scsi/scsi_scan.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 983aed1..523faee 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1593,16 +1593,15 @@ EXPORT_SYMBOL(scsi_add_device);
 
 void scsi_rescan_device(struct device *dev)
 {
-	if (!dev->driver)
-		return;
-
-	if (try_module_get(dev->driver->owner)) {
+	device_lock(dev);
+	if (dev->driver && try_module_get(dev->driver->owner)) {
 		struct scsi_driver *drv = to_scsi_driver(dev->driver);
 
 		if (drv->rescan)
 			drv->rescan(dev);
 		module_put(dev->driver->owner);
 	}
+	device_unlock(dev);
 }
 EXPORT_SYMBOL(scsi_rescan_device);
 
-- 
1.9.1