[Bug 261589] review of possible patch in xhci module for panic since td is NULL

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261589

            Bug ID: 261589
           Summary: review of possible patch in xhci module for panic
                    since td is NULL
           Product: Base System
           Version: Unspecified
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: usb
          Assignee: usb@FreeBSD.org
          Reporter: nitin.gupta981@gmail.com

Created attachment 231457
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=231457&action=edit
patch for review in xhci.c

Dear Group Member 

I came across the kernel Panic in xhci module for some of my development
activities .Issue is very random and looks like td is NULL ..
Please Review the below patch and let me know your thoughts

index e88a827..a6ce227 100644
--- a/sys/dev/usb/controller/xhci.c
+++ b/sys/dev/usb/controller/xhci.c
@@ -886,7 +886,7 @@ xhci_skip_transfer(struct usb_xfer *xfer)
 static void
 xhci_check_transfer(struct xhci_softc *sc, struct xhci_trb *trb)
 {
-       struct xhci_endpoint_ext *pepext;
+       struct xhci_endpoint_ext *pepext = NULL;
        int64_t offset;
        uint64_t td_event;
        uint32_t temp;
@@ -929,6 +929,10 @@ xhci_check_transfer(struct xhci_softc *sc, struct xhci_trb
*trb
)

        pepext = &sc->sc_hw.devs[index].endp[epno];

+       if (pepext == NULL) {
+               DPRINTF("pepext is Null\n");
+               return;
+       }
        if (pepext->trb_ep_mode != USB_EP_MODE_STREAMS) {
                stream_id = 0;
@@ -940,8 +944,8 @@ xhci_check_transfer(struct xhci_softc *sc, struct xhci_trb
*trb)

        /* try to find the USB transfer that generated the event */
        for (i = 0; i != (XHCI_MAX_TRANSFERS - 1); i++) {
-               struct usb_xfer *xfer;
-               struct xhci_td *td;
+               struct usb_xfer *xfer = NULL;
+               struct xhci_td *td = NULL;

                xfer = pepext->xfer[i + (XHCI_MAX_TRANSFERS * stream_id)];
                if (xfer == NULL)
@@ -949,6 +953,9 @@ xhci_check_transfer(struct xhci_softc *sc, struct xhci_trb
*trb)

                td = xfer->td_transfer_cache;


Regards
Nitin

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