[PATCH] solved APM bug with -rc5

From: Willy TARREAU (willy@w.ods.org)
Date: Thu Aug 01 2002 - 15:35:20 EST

On Thu, Aug 01, 2002 at 05:53:46PM +0100, Alan Cox wrote:
> Very curious indeed because someone else reported that rc3-ac5 works
> (which has the same vm86 code). In addition the vm86 handler in the
> kernel isnt actually used for APM. We make 32bit APM calls and the one
> 16bit case we do is a true return to real mode.

I finally got rid of it ! I now understand why it hanged randomly, and
why I spent lots of time adding/removing unrelated patches. It's because
in apm=power-off mode (SMP), a kernel thread is started for the apm()
function, which does bios calls. And sometimes, the bios is called from
CPU >0, which my bios doesn't like at all, thus explaining why the oopses
were corrupted.

By copying a piece of code somewhere else in the same file, I could force
apm() to be used only by CPU0. I could verify that it doesn't crash anymore,
and that I can also crash it on demand if I force CPU1.

The bonus is that I could re-enable the debug code in this function even
in SMP mode since we're sure that it runs on CPU0.

Here is the patch against 2.4.19-rc5. Marcelo, Alan, please review and apply.


diff -urN linux-2.4.19-rc5/arch/i386/kernel/apm.c linux-2.4.19-rc5-fix/arch/i386/kernel/apm.c
--- linux-2.4.19-rc5/arch/i386/kernel/apm.c Thu Aug 1 22:07:39 2002
+++ linux-2.4.19-rc5-fix/arch/i386/kernel/apm.c Thu Aug 1 22:26:56 2002
@@ -1661,6 +1661,17 @@
         strcpy(current->comm, "kapmd");
+#ifdef CONFIG_SMP
+ /* 2002/08/01 - WT
+ * This is to avoid random crashes at boot time during initialization
+ * on SMP systems in case of "apm=power-off" mode. Seen on ASUS A7M266D.
+ * Some bioses don't like being called from CPU != 0.
+ */
+ while (cpu_number_map(smp_processor_id()) != 0) {
+ schedule();
+ }
         if (apm_info.connection_version == 0) {
                 apm_info.connection_version = apm_info.bios.version;
                 if (apm_info.connection_version > 0x100) {
@@ -1707,7 +1718,7 @@
- if (debug && (smp_num_cpus == 1)) {
+ if (debug) {
                 error = apm_get_power_status(&bx, &cx, &dx);
                 if (error)
                         printk(KERN_INFO "apm: power status not available\n");
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