Is the preemptive kernel patch unsafe for 8xx/PPC?

Eugene Surovegin ebs at
Fri Dec 13 17:09:48 EST 2002


At 12:35 PM 12/12/2002, you wrote:
>Was that the 2.4.19-2 patch? What were the bugs and have you fixed them?

I had the following issues with 2.4.19-2 (2.4.20-1 is identical in this

1) arch/ppc/kernel.entry.S

diff -urN linux-2.4.20/arch/ppc/kernel/entry.S linux/arch/ppc/kernel/entry.S
--- linux-2.4.20/arch/ppc/kernel/entry.S        2002-11-28
18:53:11.000000000 -0500
+++ linux/arch/ppc/kernel/entry.S       2002-12-11 02:34:47.000000000 -0500
@@ -278,6 +278,41 @@
         cmpi    0,r3,0
         beq     restore
+       lwz     r3,PREEMPT_COUNT(r2)
+       cmpi    0,r3,1
+       bge     ret_from_except
+       lwz     r5,_MSR(r1)
+       andi.   r5,r5,MSR_PR
+       bne     do_signal_ret

     <rest of the diff is skipped>

I had to change the last command to "bne ret_from_except".
I checked MontaVista tree, and they have "ret_from_except" there also.

Without this change trivial code:

   while (true) ;

locked the box completely.

2) include/asm-ppc/pgalloc.h  There are curly brackets missing in

3) to support 440GP you have to modify arc/ppc/kernel/irc.c:preempt_intercept:

#if !defined(CONFIG_4xx) || defined(CONFIG_440)
         case 0x900:
         case 0x1000:

With these changes (an maybe some others I forgot to mention here :),
I have pretty stable preemptable kernel (2.4.19, PPC440GP & 405GP, also
with rtsched patch by George Anzinger)


  Eugene Surovegin <mailto:ebs at>

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