Re: [microblaze-uclinux] kernel BUG at sched.c:687!

[Alejandro Lucero <alucero@xxxxxxxxx>]

On Thursday 20 April 2006 13:29, Brettschneider Falk wrote:
> Hi Alejandro,
> thanks! Am I right, it will infinitely loop in case of a kernel stack
> overflow? If yes, how could I write a fixed value to a register address in
> that loop (to e.g. switch an LED on)? Going to try that soon...
> Cheers, F@lk

If the CPU executes this infinity loop it means the kernel stack size is more 
than 7500 bytes and this size is very close to 8192. Moreover, the limit is 
8192 - sizeof(struct task_struct) since the process descriptor is at the 
bottom. This does not imply a stack overflow but the odds are high.

If you know the leds address (look at 
arch/microblaze/platform/uclinux-auto/autoconfig.in) you can use it with a 
swi instruction:

	addi r11, r0, 0x1;  /* Assuming 0x00000001 put a led on */
	swi r11, r0, led_address;

You can add this before the first nop instruction.

> > -----Original Message-----
> > From: owner-microblaze-uclinux@xxxxxxxxxxxxxx
> > [mailto:owner-microblaze-uclinux@xxxxxxxxxxxxxx]On Behalf Of Alejandro
> > Lucero
> > Sent: Thursday, April 20, 2006 1:50 PM
> > To: microblaze-uclinux@xxxxxxxxxxxxxx
> > Subject: Re: [microblaze-uclinux] kernel BUG at sched.c:687!
> >
> > On Thursday 20 April 2006 10:31, Brettschneider Falk wrote:
> > > Hi,
> > >
> > > Alejandro Lucero wrote:
> > > > I assumed you are using the entry.S without my patch reported
> > > > two days ago.
> > > > aren't you?
> > >
> > > I've tried JWs version of your patch but it doesn't help as
> >
> > a bugfix. My
> >
> > > environment is one active user app with several threads
> >
> > (SCHED_RR), a high
> >
> > > IRQ frequency (about 2 per millisecond), many thread switches, many
> > > locks/unlocks of semaphores and mutexes. From time to time
> >
> > one thread of
> >
> > > that application calls pthread_cancel() to another thread.
> > > Often (about after 20 kill actions) this leads to either a
> >
> > Linux crash
> >
> > > (with several versions of "kernel BUG at sched.c:***"), or
> >
> > just a total
> >
> > > hang or an exit of the app with return code 5. (The statistical
> > > distribution is: displaying of scheduler bug = 0,01%, Linux
> >
> > hang = 60%,
> >
> > > process exit = rest.) I haven't the problems if either the
> >
> > IRQ frequency is
> >
> > > very low or no threads are cancelled(). That's why I asked
> >
> > you if you ever
> >
> > > tried to kill threads in your application, this increases
> >
> > the chance of a
> >
> > > Linux crash extremely here.
> >
> > Perhaps you could do some tests to discard the kernel stack
> > overflow. Try to
> > put this in your entry.S file but update the "current"
> > pointer and make sure
> > you are not using memory 0x554, 0x558, 0xc64 and 0xc68
> > (surely LMB memory).
> > This code looks at the kernel stack size and if it is greter
> > then 0x1d4c
> > (7500bytes) the system will execute an endless loop with
> > interrupts disabled.
> > In 0xc64 is stored the maximum kernel stack size used.
> >
> > Rembember to update current which is my kernel is in
> > 0x0213472c address. Use
> > objdump -t image.elf | grep current
> >
> > Try to put this in ENTRY(irq) just after swi r1, r0, ENTRY_SP
> > and before
> > SAVE_STATE
> >
> >        			swi r11, r0, 0x554
> > 			swi r12, r0, 0x558
> >                         lwi    r11, r0, 0x0213472c;
> >                         addi   r11, r11, 0x2000;
> >                         rsub   r11, r1, r11;
> >                         lwi    r12, r0, 0xc64;
> >                         swi    r11, r0, 0xc68;
> >                         rsub   r11, r11, r12;
> >                         bgei   r11, 1f;
> >                         lwi    r11, r0, 0xc68;
> >                         swi    r11, r0, 0xc64;
> >                         1:
> >                         lwi    r11, r0, 0x0213472c;
> >                         addi   r11, r11, 0x2000;
> >                         rsub   r11, r1, r11;
> >                         addi   r12, r0, 0x1d4c;
> >                         rsub   r11, r12, r11;
> >                         blei   r11, 2f;
> >                         lwi    r11, r0, 0;
> >                         mts    rmsr, r11;
> >                         nop;
> >                         nop;
> >                         nop;
> >                         bri -8;
> >                         2:
> > 			lwi r11, r0, 0x554
> > 			lwi r12, r0, 0x558
> >
> > > Cheers, F@lk
> > > ___________________________
> > > microblaze-uclinux mailing list
> > > microblaze-uclinux@xxxxxxxxxxxxxx
> > > Project Home Page :
>
> http://www.itee.uq.edu.au/~jwilliams/mblaze-uclinux
>
> > Mailing List Archive :
> > http://www.itee.uq.edu.au/~listarch/microblaze-uclinux/

-- 
Alejandro Lucero
Technical Director
+34 665 68 71 68
Valencia (SPAIN)
www.os3sl.com
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