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

From: Sudeep Holla
Date: Thu Mar 05 2015 - 05:52:54 EST




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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