Page fault at USB attachment code

[Farhan Khan]

On Thu, Dec 26, 2019, at 3:33 AM, Hans Petter Selasky wrote:
> On 2019-12-26 01:46, Farhan Khan wrote:
> > Hi all,
> > 
> > I am writing a simple USB network device driver skeleton, just to learn the framework. What I think is fairly simple code is having a kernel panic when it hits the attachment code.
> > 
> > The code and kgdb output are below. I apologize, its been some time since I used kgdb, so I am not sure what the next step I should do to debug this.
> > 
> > ---------------------
> > static int
> > skel_usb_attach(device_t self)
> > {
> > struct usb_attach_arg *uaa = device_get_ivars(self);
> > struct skel_usb_softc *uc = device_get_softc(self);
> > struct skel_softc *sc = uc->sc_sc;
> > struct ieee80211com *ic = &sc->sc_ic;
> > 
> > device_set_usb_desc(self);
> > uc->uc_udev = uaa->device;
> > sc->sc_dev = self;
> > ic->ic_name = device_get_nameunit(self);
> > 
> > return 0;
> > }
> > ---------------------
> > 
> > When I run kgdb, I get the following output.
> > 
> > ---------------------
> > sudo kgdb -n last
> > GNU gdb (GDB) 8.3.1 [GDB v8.3.1 for FreeBSD]
> > Copyright (C) 2019 Free Software Foundation, Inc.
> > License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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> > There is NO WARRANTY, to the extent permitted by law.
> > Type "show copying" and "show warranty" for details.
> > This GDB was configured as "x86_64-portbld-freebsd13.0".
> > Type "show configuration" for configuration details.
> > For bug reporting instructions, please see:
> > <http://www.gnu.org/software/gdb/bugs/>.
> > Find the GDB manual and other documentation resources online at:
> > <http://www.gnu.org/software/gdb/documentation/>.
> > 
> > For help, type "help".
> > Type "apropos word" to search for commands related to "word"...
> > Reading symbols from /usr/obj/usr/src/amd64.amd64/sys/GENERIC/kernel.full...
> > 
> > Unread portion of the kernel message buffer:
> > Matched!
> > skel0 on uhub0
> > skel0: <ATHEROS USB2.0 WLAN, rev 1.10/ff.ff, addr 2> on usbus0
> > 
> > Fatal trap 12: page fault while in kernel mode
> > cpuid = 0; apic id = 00
> > fault virtual address = 0x7170
> > fault code = supervisor write data, page not present
> > instruction pointer = 0x20:0xffffffff8271f094
> > stack pointer = 0x28:0xfffffe00036f5930
> > frame pointer = 0x28:0xfffffe00036f5950
> > code segment = base 0x0, limit 0xfffff, type 0x1b
> > = DPL 0, pres 1, long 1, def32 0, gran 1
> > processor eflags = interrupt enabled, resume, IOPL = 0
> > current process = 15 (usbus0)
> > trap number = 12
> > panic: page fault
> > cpuid = 0
> > time = 1577299341
> > KDB: stack backtrace:
> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00036f5590
> > vpanic() at vpanic+0x17e/frame 0xfffffe00036f55f0
> > panic() at panic+0x43/frame 0xfffffe00036f5650
> > trap_fatal() at trap_fatal+0x386/frame 0xfffffe00036f56b0
> > trap_pfault() at trap_pfault+0x99/frame 0xfffffe00036f5730
> > trap() at trap+0x2a3/frame 0xfffffe00036f5860
> > calltrap() at calltrap+0x8/frame 0xfffffe00036f5860
> > --- trap 0xc, rip = 0xffffffff8271f094, rsp = 0xfffffe00036f5930, rbp = 0xfffffe00036f5950 ---
> > skel_usb_attach() at skel_usb_attach+0x34/frame 0xfffffe00036f5950
> > device_attach() at device_attach+0x3ca/frame 0xfffffe00036f5990
> > device_probe_and_attach() at device_probe_and_attach+0x70/frame 0xfffffe00036f59c0
> > usb_probe_and_attach_sub() at usb_probe_and_attach_sub+0x150/frame 0xfffffe00036f5a10
> > usb_probe_and_attach() at usb_probe_and_attach+0x463/frame 0xfffffe00036f5ae0
> > uhub_explore() at uhub_explore+0x753/frame 0xfffffe00036f5b50
> > usb_bus_explore() at usb_bus_explore+0x11a/frame 0xfffffe00036f5b70
> > usb_process() at usb_process+0x103/frame 0xfffffe00036f5bb0
> > fork_exit() at fork_exit+0x80/frame 0xfffffe00036f5bf0
> > fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00036f5bf0
> > --- trap 0, rip = 0, rsp = 0, rbp = 0 ---
> > KDB: enter: panic
> > 
> > warning: Could not load shared library symbols for if_skel_usb.ko.
> > Do you need "set solib-search-path" or "set sysroot"?
> > ---------------------
> > 
> > Note: I am testing this with an Atheros USB device.
> > 
> > Thanks!
> > 
> 
> Are you sure you specified sizeof the correct softc, in the driver 
> declaration?
> 
> --HPS
> 
> 

Hi HPS,

It was a very silly mistake on my end. The HAL layer was not allocating memory for the skel_softc variable. This was causing "sc->sc_dev = self;" to panic.

Thank you!
--
Farhan Khan
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