Messages in this thread |  | | Date | Thu, 22 Feb 2007 15:02:46 +0000 | From | Jose Goncalves <> | Subject | Re: Serial related oops |
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Russell King wrote: > On Wed, Feb 21, 2007 at 02:13:15PM +0000, Jose Goncalves wrote: > >> <1>[18840.304048] Unable to handle kernel NULL pointer dereference at virtual address 00000012 >> <1>[18840.313046] printing eip: >> <4>[18840.321687] c01bfa7a >> <1>[18840.321714] *pde = 00000000 >> <0>[18840.331287] Oops: 0000 [#1] >> <4>[18840.340687] Modules linked in: >> <0>[18840.349749] CPU: 0 >> <4>[18840.349767] EIP: 0060:[<c01bfa7a>] Not tainted VLI >> <4>[18840.349782] EFLAGS: 00010202 (2.6.16.41-mtm5-debug1 #1) >> <0>[18840.377277] EIP is at serial_in+0xa/0x4a >> <0>[18840.387221] eax: 00000060 ebx: 00000000 ecx: 00000000 edx: 00000000 >> <0>[18840.397805] esi: 00000000 edi: 00000040 ebp: c728fe1c esp: c728fe18 >> <0>[18840.408579] ds: 007b es: 007b ss: 0068 >> <0>[18840.419624] Process gp_position (pid: 11629, threadinfo=c728e000 task=c7443a90) >> <0>[18840.420509] Stack: <0>00000000 00000000 c01c0f88 00000000 00000000 c031fef0 00000005 00000202 >> <0>[18840.445655] c7161a1c c031fef0 c124b510 c728fe60 c01bd97d c031fef0 c124b510 c124b510 >> <0>[18840.460540] 00000000 c773dbcc c728fe7c c01befe7 c124b510 00000000 ffffffed c773dbcc >> > > Okay, this one is even more plainly "not a coding error". > > >> <0>[18840.566645] [<c01c0f88>] serial8250_startup+0x28f/0x2a9 >> > > The code around this point (with the return point marked) is: > > >> c01c0f78: 6a 05 push $0x5 >> c01c0f7a: 53 push %ebx >> c01c0f7b: e8 f0 ea ff ff call c01bfa70 <serial_in> >> c01c0f80: 6a 00 push $0x0 >> c01c0f82: 53 push %ebx >> c01c0f83: e8 e8 ea ff ff call c01bfa70 <serial_in> >> c01c0f88<<< 6a 02 push $0x2 >> c01c0f8a: 53 push %ebx >> c01c0f8b: e8 e0 ea ff ff call c01bfa70 <serial_in> >> > > and corresponds with this C code: > > (void) serial_inp(up, UART_LSR); > (void) serial_inp(up, UART_RX); > (void) serial_inp(up, UART_IIR); > > Now let's look at the words pushed on the stack around this code: > > 00000000 > 00000000 > c01c0f88 <- return address for serial_in (serial8250_startup+0x28f/0x2a9) > 00000000 <- from push %ebx at c01c0f82 > 00000000 <- from push $0x0 at c01c0f80 > c031fef0 <- from push %ebx at c01c0f7a > 00000005 <- from push %0x5 at c01c0f78 > > Plainly, %ebx changed across the call to serial_in() at c01c0f7b. > First thing to notice is this violates the C code - "up" can not > change. > > Now let's look at serial_in: > > c01bfa70: 55 push %ebp > c01bfa71: 89 e5 mov %esp,%ebp > c01bfa73: 53 push %ebx > ... > c01bfab7: 5b pop %ebx > c01bfab8: 5d pop %ebp > c01bfab9: c3 ret > > This code tells the CPU to preserves %ebx and %ebp. But we know %ebx > _wasn't_ preserved. Ergo, your CPU is plainly not doing what the code > told it to do. > > Moreover, serial_in() has preserved %ebx in the past otherwise we'd > never got past all the other serial_in()s in serial8250_startup(). > > So I think it's very demonstrably a hardware fault, and not software > related. >
It could be a silly question (tamper with me as I'm not familiar with such low level programming), but couldn't it be possible for a interrupt to hit in the middle of the serial_in() calls and mess with %ebx?
What I find real hard to understand is why a hardware fault happens always in the same software instruction! I would expect a hardware fault to hit randomly...
I left my application running this night, with a 2.6.16.41 kernel unpatched on the serial driver (my last Oops report was with Frederik patch to remove the insertion made in 2.6.12) and it crashed again on exactly the same point!
> For all we know, it could be a one-off fault on the hardware you > happen to have - other identical units may not behave the same (can > you check?) >
Yes I have other units that I can test it. I'll do that to see if it's really a one-off fault on the hardware. If it continues to crash with other units I will then test with the msleep(10) before the "And clear the interrupt registers again for luck.", as you suggested earlier.
> If it is a one off case, you are welcome to patch that test out in > your kernel build to remove the problem, and if it's an isolated case > I encourage you to do this. This is one of the great advantages of > open source - if you hit such a problem rather than throwing the > hardware away you can work around such issues. >
I didn't understand what you mean by "you are welcome to patch that test out in your kernel build to remove the problem". Which test are you talking about?
Regards, José Gonçalves
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