Re: [PATCH] usb: isp1760: fix possible deadlock in isp1760_udc_irq

[Sudeep Holla <sudeep.holla@arm.com>]

On 05/03/15 10:49, Laurent Pinchart wrote:
> Hi Sudeep,
>
> Thank you for the patch.
>
> On Wednesday 04 March 2015 17:07:57 Sudeep Holla wrote:
>> Use spin_{un,}lock_irq{save,restore} in isp1760_udc_{start,stop} to
>> prevent following potentially deadlock scenario between
>> isp1760_udc_{start,stop} and isp1760_udc_irq :
>>
>> =================================
>> [ INFO: inconsistent lock state ]
>> 4.0.0-rc2-00004-gf7bb2ef60173 #51 Not tainted
>> ---------------------------------
>> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
>> in:imklog/2118 [HC1[1]:SC0[0]:HE0:SE1] takes:
>>   (&(&udc->lock)->rlock){?.+...}, at: [<c0397a93>]
>> isp1760_udc_irq+0x367/0x9dc {HARDIRQ-ON-W} state was registered at:
>>    [<c05135b3>] _raw_spin_lock+0x23/0x30
>>    [<c0396b87>] isp1760_udc_start+0x23/0xf8
>>    [<c039dc21>] udc_bind_to_driver+0x71/0xb0
>>    [<c039de4f>] usb_gadget_probe_driver+0x53/0x9c
>>    [<bf80d0df>] usb_composite_probe+0x8a/0xa4 [libcomposite]
>>    [<bf8311a7>] 0xbf8311a7
>>    [<c00088c5>] do_one_initcall+0x8d/0x17c
>>    [<c050b92d>] do_init_module+0x49/0x148
>>    [<c0087323>] load_module+0xb7f/0xbc4
>>    [<c0087471>] SyS_finit_module+0x51/0x74
>>    [<c000d8c1>] ret_fast_syscall+0x1/0x68
>> irq event stamp: 4966
>> hardirqs last  enabled at (4965): [<c05137df>]
>> _raw_spin_unlock_irq+0x1f/0x24 hardirqs last disabled at (4966):
>> [<c00110b3>] __irq_svc+0x33/0x64 softirqs last  enabled at (4458):
>> [<c0023475>] __do_softirq+0x23d/0x2d0 softirqs last disabled at (4389):
>> [<c002380b>] irq_exit+0xef/0x15c
>>
>> other info that might help us debug this:
>>   Possible unsafe locking scenario:
>>
>>         CPU0
>>         ----
>>    lock(&(&udc->lock)->rlock);
>>    <Interrupt>
>>      lock(&(&udc->lock)->rlock);
>>
>>   *** DEADLOCK ***
>>
>> 1 lock held by in:imklog/2118:
>>   #0:  (&f->f_pos_lock){+.+.+.}, at: [<c010a101>] __fdget_pos+0x31/0x34
>>
>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: Felipe Balbi <balbi@ti.com>
>> ---
>>   drivers/usb/isp1760/isp1760-udc.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/isp1760/isp1760-udc.c
>> b/drivers/usb/isp1760/isp1760-udc.c index 6d618b3fab07..fbfbd59aae64 100644
>> --- a/drivers/usb/isp1760/isp1760-udc.c
>> +++ b/drivers/usb/isp1760/isp1760-udc.c
>> @@ -1191,6 +1191,7 @@ static int isp1760_udc_start(struct usb_gadget
>> *gadget, struct usb_gadget_driver *driver)
>>   {
>>   	struct isp1760_udc *udc = gadget_to_udc(gadget);
>> +	unsigned long flags;
>>
>>   	/* The hardware doesn't support low speed. */
>>   	if (driver->max_speed < USB_SPEED_FULL) {
>> @@ -1198,7 +1199,7 @@ static int isp1760_udc_start(struct usb_gadget
>> *gadget, return -EINVAL;
>>   	}
>>
>> -	spin_lock(&udc->lock);
>> +	spin_lock_irqsave(&udc->lock, flags);
>
> Strictly speaking spin_lock_irq() should be enough given that udc_start and
> udc_stop are called with interrupts enabled, but I suppose it doesn't hurt to
> be safe. I'll let you go with your preference. For both options,
>

I agree, even I had similar thoughts but just played safe :)

> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>

Thanks.

--
Regars,
Sudeep