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USB: dummy-hcd: Fix erroneous synchronization change 

A recent change to the synchronization in dummy-hcd was incorrect.
The issue was that dummy_udc_stop() contained no locking and therefore
could race with various gadget driver callbacks, and the fix was to
add locking and issue the callbacks with the private spinlock held.

UDC drivers aren't supposed to do this.  Gadget driver callback
routines are allowed to invoke functions in the UDC driver, and these
functions will generally try to acquire the private spinlock.  This
would deadlock the driver.

The correct solution is to drop the spinlock before issuing callbacks,
and avoid races by emulating the synchronize_irq() call that all real
UDC drivers must perform in their ->udc_stop() routines after
disabling interrupts.  This involves adding a flag to dummy-hcd's
private structure to keep track of whether interrupts are supposed to
be enabled, and adding a counter to keep track of ongoing callbacks so
that dummy_udc_stop() can wait for them all to finish.

A real UDC driver won't receive disconnect, reset, suspend, resume, or
setup events once it has disabled interrupts.  dummy-hcd will receive
them but won't try to issue any gadget driver callbacks, which should
be just as good.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Fixes: f16443a034 ("USB: gadgetfs, dummy-hcd, net2280: fix locking for callbacks")
CC: <stable@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
This commit is contained in:
Alan Stern 2017-09-26 15:15:49 -04:00 committed by Felipe Balbi
parent 0173a68bfb
commit 7dbd8f4cab
1 changed files with 30 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
drivers/usb/gadget/udc/dummy_hcd.c
View File

@ -255,11 +255,13 @@ struct dummy {
*/
struct dummy_ep ep[DUMMY_ENDPOINTS];
int address;
int callback_usage;
struct usb_gadget gadget;
struct usb_gadget_driver *driver;
struct dummy_request fifo_req;
u8 fifo_buf[FIFO_SIZE];
u16 devstatus;
unsigned ints_enabled:1;
unsigned udc_suspended:1;
unsigned pullup:1;
@ -441,18 +443,27 @@ static void set_link_state(struct dummy_hcd *dum_hcd)
(~dum_hcd->old_status) & dum_hcd->port_status;
/* Report reset and disconnect events to the driver */
if (dum->driver && (disconnect || reset)) {
if (dum->ints_enabled && (disconnect || reset)) {
stop_activity(dum);
++dum->callback_usage;
spin_unlock(&dum->lock);
if (reset)
usb_gadget_udc_reset(&dum->gadget, dum->driver);
else
dum->driver->disconnect(&dum->gadget);
spin_lock(&dum->lock);
--dum->callback_usage;
}
} else if (dum_hcd->active != dum_hcd->old_active) {
} else if (dum_hcd->active != dum_hcd->old_active &&
dum->ints_enabled) {
++dum->callback_usage;
spin_unlock(&dum->lock);
if (dum_hcd->old_active && dum->driver->suspend)
dum->driver->suspend(&dum->gadget);
else if (!dum_hcd->old_active && dum->driver->resume)
dum->driver->resume(&dum->gadget);
spin_lock(&dum->lock);
--dum->callback_usage;
}
dum_hcd->old_status = dum_hcd->port_status;
@ -973,8 +984,11 @@ static int dummy_udc_start(struct usb_gadget *g,
* can't enumerate without help from the driver we're binding.
*/
spin_lock_irq(&dum->lock);
dum->devstatus = 0;
dum->driver = driver;
dum->ints_enabled = 1;
spin_unlock_irq(&dum->lock);
return 0;
}
@ -985,6 +999,16 @@ static int dummy_udc_stop(struct usb_gadget *g)
struct dummy *dum = dum_hcd->dum;
spin_lock_irq(&dum->lock);
dum->ints_enabled = 0;
stop_activity(dum);
/* emulate synchronize_irq(): wait for callbacks to finish */
while (dum->callback_usage > 0) {
spin_unlock_irq(&dum->lock);
usleep_range(1000, 2000);
spin_lock_irq(&dum->lock);
}
dum->driver = NULL;
spin_unlock_irq(&dum->lock);
@ -1529,6 +1553,8 @@ static struct dummy_ep *find_endpoint(struct dummy *dum, u8 address)
if (!is_active((dum->gadget.speed == USB_SPEED_SUPER ?
dum->ss_hcd : dum->hs_hcd)))
return NULL;
if (!dum->ints_enabled)
return NULL;
if ((address & ~USB_DIR_IN) == 0)
return &dum->ep[0];
for (i = 1; i < DUMMY_ENDPOINTS; i++) {
@ -1870,10 +1896,12 @@ static void dummy_timer(unsigned long _dum_hcd)
* until setup() returns; no reentrancy issues etc.
*/
if (value > 0) {
++dum->callback_usage;
spin_unlock(&dum->lock);
value = dum->driver->setup(&dum->gadget,
&setup);
spin_lock(&dum->lock);
--dum->callback_usage;
if (value >= 0) {
/* no delays (max 64KB data stage) */