usb: gadget: udc: core: Fix error case while binding pending gadget drivers

If binding a pending gadget driver fails we should not
remove it from the pending driver list, otherwise it
will cause a segmentation fault later when the gadget driver is
unloaded.

Test case:

- Make sure no UDC is available
- modprobe g_mass_storage file=wrongfile
- Load UDC driver so it becomes available
	lun0: unable to open backing file: wrongfile
- modprobe -r g_mass_storage

[   60.900431] Unable to handle kernel paging request at virtual address dead000000000108
[   60.908346] Mem abort info:
[   60.911145]   ESR = 0x96000044
[   60.914227]   Exception class = DABT (current EL), IL = 32 bits
[   60.920162]   SET = 0, FnV = 0
[   60.923217]   EA = 0, S1PTW = 0
[   60.926354] Data abort info:
[   60.929228]   ISV = 0, ISS = 0x00000044
[   60.933058]   CM = 0, WnR = 1
[   60.936011] [dead000000000108] address between user and kernel address ranges
[   60.943136] Internal error: Oops: 96000044 [#1] PREEMPT SMP
[   60.948691] Modules linked in: g_mass_storage(-) usb_f_mass_storage libcomposite xhci_plat_hcd xhci_hcd usbcore ti_am335x_adc kfifo_buf omap_rng cdns3 rng_core udc_core crc32_ce xfrm_user crct10dif_ce snd_so6
[   60.993995] Process modprobe (pid: 834, stack limit = 0x00000000c2aebc69)
[   61.000765] CPU: 0 PID: 834 Comm: modprobe Not tainted 4.19.59-01963-g065f42a60499 #92
[   61.008658] Hardware name: Texas Instruments SoC (DT)
[   61.014472] pstate: 60000005 (nZCv daif -PAN -UAO)
[   61.019253] pc : usb_gadget_unregister_driver+0x7c/0x108 [udc_core]
[   61.025503] lr : usb_gadget_unregister_driver+0x30/0x108 [udc_core]
[   61.031750] sp : ffff00001338fda0
[   61.035049] x29: ffff00001338fda0 x28: ffff800846d40000
[   61.040346] x27: 0000000000000000 x26: 0000000000000000
[   61.045642] x25: 0000000056000000 x24: 0000000000000800
[   61.050938] x23: ffff000008d7b0d0 x22: ffff0000088b07c8
[   61.056234] x21: ffff000001100000 x20: ffff000002020260
[   61.061530] x19: ffff0000010ffd28 x18: 0000000000000000
[   61.066825] x17: 0000000000000000 x16: 0000000000000000
[   61.072121] x15: 0000000000000000 x14: 0000000000000000
[   61.077417] x13: ffff000000000000 x12: ffffffffffffffff
[   61.082712] x11: 0000000000000030 x10: 7f7f7f7f7f7f7f7f
[   61.088008] x9 : fefefefefefefeff x8 : 0000000000000000
[   61.093304] x7 : ffffffffffffffff x6 : 000000000000ffff
[   61.098599] x5 : 8080000000000000 x4 : 0000000000000000
[   61.103895] x3 : ffff000001100020 x2 : ffff800846d40000
[   61.109190] x1 : dead000000000100 x0 : dead000000000200
[   61.114486] Call trace:
[   61.116922]  usb_gadget_unregister_driver+0x7c/0x108 [udc_core]
[   61.122828]  usb_composite_unregister+0x10/0x18 [libcomposite]
[   61.128643]  msg_cleanup+0x18/0xfce0 [g_mass_storage]
[   61.133682]  __arm64_sys_delete_module+0x17c/0x1f0
[   61.138458]  el0_svc_common+0x90/0x158
[   61.142192]  el0_svc_handler+0x2c/0x80
[   61.145926]  el0_svc+0x8/0xc
[   61.148794] Code: eb03003f d10be033 54ffff21 a94d0281 (f9000420)
[   61.154869] ---[ end trace afb22e9b637bd9a7 ]---
Segmentation fault

Signed-off-by: Roger Quadros <rogerq@ti.com>

---
 drivers/usb/gadget/udc/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

On Wed, 21 Aug 2019, Roger Quadros wrote:

> If binding a pending gadget driver fails we should not

> remove it from the pending driver list, otherwise it

> will cause a segmentation fault later when the gadget driver is

> unloaded.


> Signed-off-by: Roger Quadros <rogerq@ti.com>

> ---

>  drivers/usb/gadget/udc/core.c | 2 +-

>  1 file changed, 1 insertion(+), 1 deletion(-)

> 

> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c

> index 7cf34beb50df..c272c8014772 100644

> --- a/drivers/usb/gadget/udc/core.c

> +++ b/drivers/usb/gadget/udc/core.c

> @@ -1142,7 +1142,7 @@ static int check_pending_gadget_drivers(struct usb_udc *udc)

>  		if (!driver->udc_name || strcmp(driver->udc_name,

>  						dev_name(&udc->dev)) == 0) {

>  			ret = udc_bind_to_driver(udc, driver);

> -			if (ret != -EPROBE_DEFER)

> +			if (!ret)

>  				list_del(&driver->pending);

>  			break;

>  		}


This is kind of a policy question.  If binding a pending gadget driver 
fails, should the driver remain pending?

Depending on the answer to this question, you might want to change the 
list_del to list_del_init.  That should fix the segmentation fault 
just as well.

Alan Stern

On 21/08/2019 17:30, Alan Stern wrote:
> On Wed, 21 Aug 2019, Roger Quadros wrote:

> 

>> If binding a pending gadget driver fails we should not

>> remove it from the pending driver list, otherwise it

>> will cause a segmentation fault later when the gadget driver is

>> unloaded.

> 

>> Signed-off-by: Roger Quadros <rogerq@ti.com>

>> ---

>>  drivers/usb/gadget/udc/core.c | 2 +-

>>  1 file changed, 1 insertion(+), 1 deletion(-)

>>

>> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c

>> index 7cf34beb50df..c272c8014772 100644

>> --- a/drivers/usb/gadget/udc/core.c

>> +++ b/drivers/usb/gadget/udc/core.c

>> @@ -1142,7 +1142,7 @@ static int check_pending_gadget_drivers(struct usb_udc *udc)

>>  		if (!driver->udc_name || strcmp(driver->udc_name,

>>  						dev_name(&udc->dev)) == 0) {

>>  			ret = udc_bind_to_driver(udc, driver);

>> -			if (ret != -EPROBE_DEFER)

>> +			if (!ret)

>>  				list_del(&driver->pending);

>>  			break;

>>  		}

> 

> This is kind of a policy question.  If binding a pending gadget driver 

> fails, should the driver remain pending?

> 

> Depending on the answer to this question, you might want to change the 

> list_del to list_del_init.  That should fix the segmentation fault 

> just as well.


OK. I'll send a revised patch to retain existing policy.

cheers,
-roger
-- 
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki