[PATCH] solved APM bug with -rc5 (take 2)

From: Willy TARREAU (willy@w.ods.org)
Date: Thu Aug 01 2002 - 19:12:58 EST

On Thu, Aug 01, 2002 at 11:16:23PM +0100, Alan Cox wrote:
> On Thu, 2002-08-01 at 21:35, Willy TARREAU wrote:
> > +#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();
> > + }
> > +#endif
>
> What guarantees that loop will ever exit ?

I asked Ingo for some advice, and he gently sent me a piece of code as an
example of how to reliably bind a task to a CPU. I tried it, and it's OK here.
I could reliably switch several times from cpu0 to cpu1, then back to cpu0.
Since it was cleaner than the previous method, I also did the same for
apm_power_off(), thus getting rid of apm_magic() and its dedicated thread.
Then again, I tested with multiple cpu switches, and every time, my system
correctly handles the case. I'm writing this mail under 2.4.19-rc5.

So here is the patch against 2.4.19-rc5, hoping it will get in this time.
I think it should apply without a glitch to 2.4.19-rc5-ac1, but don't
know about 2.5, nor even if it is needed.

Feedback welcome, of course ;-)

Cheers,
Willy

--- 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 Fri Aug 2 01:52:55 2002
@@ -862,14 +862,6 @@
                 apm_do_busy();
 }
 
-#ifdef CONFIG_SMP
-static int apm_magic(void * unused)
-{
- while (1)
- schedule();
-}
-#endif
-
 /**
  * apm_power_off - ask the BIOS to power off
  *
@@ -897,10 +889,11 @@
          */
 #ifdef CONFIG_SMP
         /* Some bioses don't like being called from CPU != 0 */
- while (cpu_number_map(smp_processor_id()) != 0) {
- kernel_thread(apm_magic, NULL,
- CLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD);
+ if (cpu_number_map(smp_processor_id()) != 0) {
+ current->cpus_allowed = 1;
                 schedule();
+ if (unlikely(cpu_number_map(smp_processor_id()) != 0))
+ BUG();
         }
 #endif
         if (apm_info.realmode_power_off)
@@ -1661,6 +1654,21 @@
         strcpy(current->comm, "kapmd");
         sigfillset(&current->blocked);
 
+#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.
+ * Method suggested by Ingo Molnar.
+ */
+ if (cpu_number_map(smp_processor_id()) != 0) {
+ current->cpus_allowed = 1;
+ schedule();
+ if (unlikely(cpu_number_map(smp_processor_id()) != 0))
+ BUG();
+ }
+#endif
+
         if (apm_info.connection_version == 0) {
                 apm_info.connection_version = apm_info.bios.version;
                 if (apm_info.connection_version > 0x100) {
@@ -1707,7 +1715,7 @@
                 }
         }
 
- 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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