On 18/05/16 15:56, Alan Stern wrote:
On Wed, 18 May 2016, Srinivas Kandagatla wrote:
This patch adds a check in ehci_shutdown(), to make sure
that the register access is available before accessing registers.
The use case is simple, for boards like DB410c where the usb host
or device functionality is decided based on the micro-usb cable
presence. If the board boots up with micro-usb connected and the
host driver is probed, but the ehci_setup() has not been done yet,
then a system shutdown would trigger below NULL pointer exception
without this patch.
How can that happen? While the host driver is probed, the probing
thread holds the device lock. But the system shutdown routine acquires
the device lock before invoking the ->shutdown callback. Therefore the
two things cannot happen concurrently.
No, I did not mean them happening concurrently, I mean that the host
driver is up, however ehci_setup() is not done yet.
Will change the comments if its misleading the reader.
Unable to handle kernel NULL pointer dereference at virtual address
00000008
...
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -368,6 +368,9 @@ static void ehci_shutdown(struct usb_hcd *hcd)
{
struct ehci_hcd *ehci = hcd_to_ehci(hcd);
+ if (!HCD_HW_ACCESSIBLE(hcd))
+ return;
+
spin_lock_irq(&ehci->lock);
ehci->shutdown = true;
ehci->rh_state = EHCI_RH_STOPPING;
This doesn't seem like the right place. What you really should do is
skip calling ehci_silence_controller() if the hardware isn't
accessible. That's where the hardware gets touched, not in
ehci_shutdown().
Yep , that should work as well.
Will send a v2 patch.
thanks,
srini
Alan Stern
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