[PATCH] alpha: SMP boot fixes
Brian Uhrain says [Tue, 11 Apr 2006 05:53:16 +0000 (22:53 -0700)]
I've encountered two problems with 2.6.16 and newer kernels on my API CS20
(dual 833MHz Alpha 21264b processors).  The first is the kernel OOPSing
because of a NULL pointer dereference while trying to populate SysFS with the
CPU information.  The other is that only one processor was being brought up.
I've included a small Alpha-specific patch that fixes both problems.

The first problem was caused by the CPUs never being properly registered using
register_cpu(), the way it's done on other architectures.

The second problem has to do with the removal of hwrpb_cpu_present_mask in
arch/alpha/kernel/smp.c.  In setup_smp() in the 2.6.15 kernel sources,
hwrpb_cpu_present_mask has a bit set for each processor that is probed, and
afterwards cpu_present_mask is set to the cpumask for the boot CPU.  In the
same function of the same file in the 2.6.16 sources, instead of
hwrpb_cpu_present_mask being set, cpu_possible_map is updated for each probed
CPU.  cpu_present_mask is still set to the cpumask of the boot CPU afterwards.
 The problem lies in include/asm-alpha/smp.h, where cpu_possible_map is
#define'd to be cpu_present_mask.

Cleanups from: Ivan Kokshaysky <ink@jurassic.park.msu.ru>

 - cpu_present_mask and cpu_possible_map are essentially the same thing
   on alpha, as it doesn't support CPU hotplug;
 - allocate "struct cpu" only for present CPUs, like sparc64 does.
   Static array of "struct cpu" is just a waste of memory.

Signed-off-by: Brian Uhrain <buhrain@rosettastone.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/alpha/kernel/setup.c
arch/alpha/kernel/smp.c

index a15e18a..558b833 100644 (file)
@@ -24,6 +24,7 @@
 #include <linux/config.h>      /* CONFIG_ALPHA_LCA etc */
 #include <linux/mc146818rtc.h>
 #include <linux/console.h>
+#include <linux/cpu.h>
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/string.h>
@@ -471,6 +472,22 @@ page_is_ram(unsigned long pfn)
        return 0;
 }
 
+static int __init
+register_cpus(void)
+{
+       int i;
+
+       for_each_possible_cpu(i) {
+               struct cpu *p = kzalloc(sizeof(*p), GFP_KERNEL);
+               if (!p)
+                       return -ENOMEM;
+               register_cpu(p, i, NULL);
+       }
+       return 0;
+}
+
+arch_initcall(register_cpus);
+
 void __init
 setup_arch(char **cmdline_p)
 {
index 02c2db0..1852554 100644 (file)
@@ -439,7 +439,7 @@ setup_smp(void)
                        if ((cpu->flags & 0x1cc) == 0x1cc) {
                                smp_num_probed++;
                                /* Assume here that "whami" == index */
-                               cpu_set(i, cpu_possible_map);
+                               cpu_set(i, cpu_present_mask);
                                cpu->pal_revision = boot_cpu_palrev;
                        }
 
@@ -450,9 +450,8 @@ setup_smp(void)
                }
        } else {
                smp_num_probed = 1;
-               cpu_set(boot_cpuid, cpu_possible_map);
+               cpu_set(boot_cpuid, cpu_present_mask);
        }
-       cpu_present_mask = cpumask_of_cpu(boot_cpuid);
 
        printk(KERN_INFO "SMP: %d CPUs probed -- cpu_present_mask = %lx\n",
               smp_num_probed, cpu_possible_map.bits[0]);
@@ -488,9 +487,8 @@ void __devinit
 smp_prepare_boot_cpu(void)
 {
        /*
-        * Mark the boot cpu (current cpu) as both present and online
+        * Mark the boot cpu (current cpu) as online
         */ 
-       cpu_set(smp_processor_id(), cpu_present_mask);
        cpu_set(smp_processor_id(), cpu_online_map);
 }