On Fri, 27 Nov 2009, Ondrej Zary wrote: > Hello, > I have problems debbugging an oops. It happens when Nexio USB touchscreen > (using my new code http://lkml.org/lkml/2009/11/25/568) is disconnected: > > BUG: unable to handle kernel NULL pointer dereference at 00000048 > IP: [<f7c38afd>] start_unlink_async+0xb2/0x160 [ehci_hcd] ... > It does not happen everytime - sometimes it survives the first disconnect. > Tried adding printk()s to start_unlink_async function - and the oops does not appear. > Looks like a race. It might be a bug in my code but I'm not able to find it. > > It also happens only when the touchscreen is connected through a hub: > Bus 001 Device 002: ID 2001:f103 D-Link Corp. [hex] DUB-H7 7-port USB 2.0 hub > When connected directly to the machine, it does not oops. That's understandable, since the stack trace showed that the oops occurred while the hub driver was running. > Tried decodecode: > Code: 00 fb e9 bb 00 00 00 c6 46 68 02 89 f0 e8 ee e8 ff ff 85 db 89 c7 89 43 18 75 06 68 c5 e4 c3 f7 e8 b4 5f 68 c9 50 8b 43 14 89 c6 <8b> 40 48 39 f8 75 > f7 85 f6 75 0b 68 0c e5 c3 f7 e8 99 5f 68 c9 > All code > ======== > 0: 00 fb add %bh,%bl > 2: e9 bb 00 00 00 jmp 0xc2 > 7: c6 46 68 02 movb $0x2,0x68(%esi) > b: 89 f0 mov %esi,%eax > d: e8 ee e8 ff ff call 0xffffe900 > 12: 85 db test %ebx,%ebx > 14: 89 c7 mov %eax,%edi > 16: 89 43 18 mov %eax,0x18(%ebx) > 19: 75 06 jne 0x21 > 1b: 68 c5 e4 c3 f7 push $0xf7c3e4c5 > 20: e8 b4 5f 68 c9 call 0xc9685fd9 > 25: 50 push %eax > 26: 8b 43 14 mov 0x14(%ebx),%eax > 29: 89 c6 mov %eax,%esi > 2b:* 8b 40 48 mov 0x48(%eax),%eax <-- trapping instruction > 2e: 39 f8 cmp %edi,%eax > 30: 75 f7 jne 0x29 > 32: 85 f6 test %esi,%esi > 34: 75 0b jne 0x41 > 36: 68 0c e5 c3 f7 push $0xf7c3e50c > 3b: e8 99 5f 68 c9 call 0xc9685fd9 > > Code starting with the faulting instruction > =========================================== > 0: 8b 40 48 mov 0x48(%eax),%eax > 3: 39 f8 cmp %edi,%eax > 5: 75 f7 jne 0xfffffffe > 7: 85 f6 test %esi,%esi > 9: 75 0b jne 0x16 > b: 68 0c e5 c3 f7 push $0xf7c3e50c > 10: e8 99 5f 68 c9 call 0xc9685fae > > and "make drivers/usb/host/ehci-hcd.s" but I'm not able to find the above code in ehci-hcd.s. > > What am I doing wrong? With your disassembly? Nothing that I can see. You might be able to locate the code in question by comparing the output above and the contents of ehci-hcd.s with the output of "objdump -D drivers/usb/host/ehci-hcd.o" -- search for the start of the start_unlink_async() routine and go forward from there. For what it's worth, your disassembly doesn't bear any relation to the code for start_unlink_async() on my system. As for what your driver is doing wrong... Perhaps it is writing to a memory area after freeing it. Have you tried using usbmon to see what's going on before the oops occurs? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
