Felipe:
Can you check the reasoning here? I don't understand how an OTG
event could cause dwc3 to remove the shared (SuperSpeed) hcd and then
re-instantiate it before removing the primary (HS-FS-LS) hcd, which is
what this diagram seems to show.
On Wed, 8 Jun 2016, Chung-Geol Kim wrote:
> Thank you for clear understanding the problem that I faced.
> When I tested with your below patch, it also works well.
> The description has been modified as follows as you suggested.
>
> =================================================
> At *remove USB(3.0) Storage
> sequence <1> --> <5> ((Problem Case))
> =================================================
> VOLD
> ------------------------------------|------------
> (uevent)
> ________|_________
> |<1> |
> |dwc3_otg_sm_work |
> |usb_put_hcd |
> |peer_hcd(kref=2)|
> |__________________|
> ________|_________
> |<2> |
> |New USB BUS #2 |
> | |
> |peer_hcd(kref=1)|
> | |
> --(Link)-bandXX_mutex|
> | |__________________|
> |
> ___________________ |
> |<3> | |
> |dwc3_otg_sm_work | |
> |usb_put_hcd | |
> |primary_hcd(kref=1)| |
> |___________________| |
> _________|_________ |
> |<4> | |
> |New USB BUS #1 | |
> |hcd_release | |
> |primary_hcd(kref=0)| |
> | | |
> |bandXX_mutex(free) |<-
> |___________________|
> (( VOLD ))
> ______|___________
> |<5> |
> | SCSI |
> |usb_put_hcd |
> |peer_hcd(kref=0)|
> |*hcd_release |
> |bandXX_mutex(free*)|<- double free
> |__________________|
>
> =================================================
As far as I can tell, the real problem occurs when the HS/FS/LS primary
hcd is released before the SS shared hcd. The bandwidth_mutex gets
deallocated when the primary hcd is released, even though the shared
hcd still exists. Then when the shared hcd is released, it tries the
deallocate the bandwidth_mutex a second time, because the code is
written in such a way that it now thinks the shared hcd _is_ the
primary.
Is the patch below a good way to fix the problem? There doesn't _seem_
to be any harm in making this change. At least, I don't think it will
confuse drivers any more than they are already.
Thanks,
Alan Stern
Index: usb-4.x/drivers/usb/core/hcd.c
===================================================================
--- usb-4.x.orig/drivers/usb/core/hcd.c
+++ usb-4.x/drivers/usb/core/hcd.c
@@ -2588,24 +2588,22 @@ EXPORT_SYMBOL_GPL(usb_create_hcd);
* Don't deallocate the bandwidth_mutex until the last shared usb_hcd is
* deallocated.
*
- * Make sure to only deallocate the bandwidth_mutex when the primary HCD is
- * freed. When hcd_release() is called for either hcd in a peer set
- * invalidate the peer's ->shared_hcd and ->primary_hcd pointers to
- * block new peering attempts
+ * Make sure to deallocate the bandwidth_mutex only when the last HCD is
+ * freed. When hcd_release() is called for either hcd in a peer set,
+ * invalidate the peer's ->shared_hcd and ->primary_hcd pointers.
*/
static void hcd_release(struct kref *kref)
{
struct usb_hcd *hcd = container_of (kref, struct usb_hcd, kref);
mutex_lock(&usb_port_peer_mutex);
- if (usb_hcd_is_primary_hcd(hcd))
- kfree(hcd->bandwidth_mutex);
if (hcd->shared_hcd) {
struct usb_hcd *peer = hcd->shared_hcd;
peer->shared_hcd = NULL;
- if (peer->primary_hcd == hcd)
- peer->primary_hcd = NULL;
+ peer->primary_hcd = NULL;
+ } else {
+ kfree(hcd->bandwidth_mutex);
}
mutex_unlock(&usb_port_peer_mutex);
kfree(hcd);
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