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

[Sudeep Holla]

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@xxxxxxx>
> > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Felipe Balbi <balbi@xxxxxx>
> > ---
> >   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@xxxxxxxxxxxxxxxx>

Thanks.

--
Regars,
Sudeep

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