i386: Fix double fault handler

The new percpu code has apparently broken the doublefault handler
when CONFIG_DEBUG_SPINLOCK is set. Doublefault is handled by
a hardware task, making the check

        SPIN_BUG_ON(lock->owner == current, lock, "recursion");

fault because it uses the FS register to access the percpu data
for current, and that register is zero in the new TSS. (The trace
I saw was on 2.6.20 where it was GS, but it looks like this will
still happen with FS on 2.6.22.)

Initializing FS in the doublefault_tss should fix it.

AK: Also fix broken ptr_ok() and turn printks into KERN_EMERG
AK: And add a PANIC prefix to make clear the system will hang
AK: (e.g. x86-64 will recover)

Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/arch/i386/kernel/doublefault.c b/arch/i386/kernel/doublefault.c
index 265c5597efb0..40978af630e7 100644
--- a/arch/i386/kernel/doublefault.c
+++ b/arch/i386/kernel/doublefault.c
@@ -13,7 +13,7 @@
 static unsigned long doublefault_stack[DOUBLEFAULT_STACKSIZE];
 #define STACK_START (unsigned long)(doublefault_stack+DOUBLEFAULT_STACKSIZE)
 
-#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + 0x1000000)
+#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM)
 
 static void doublefault_fn(void)
 {
@@ -23,23 +23,23 @@ static void doublefault_fn(void)
         store_gdt(&gdt_desc);
         gdt = gdt_desc.address;
 
-        printk("double fault, gdt at %08lx [%d bytes]\n", gdt, gdt_desc.size);
+        printk(KERN_EMERG "PANIC: double fault, gdt at %08lx [%d bytes]\n", gdt, gdt_desc.size);
 
         if (ptr_ok(gdt)) {
                 gdt += GDT_ENTRY_TSS << 3;
                 tss = *(u16 *)(gdt+2);
                 tss += *(u8 *)(gdt+4) << 16;
                 tss += *(u8 *)(gdt+7) << 24;
-                printk("double fault, tss at %08lx\n", tss);
+                printk(KERN_EMERG "double fault, tss at %08lx\n", tss);
 
                 if (ptr_ok(tss)) {
                         struct i386_hw_tss *t = (struct i386_hw_tss *)tss;
 
-                        printk("eip = %08lx, esp = %08lx\n", t->eip, t->esp);
+                        printk(KERN_EMERG "eip = %08lx, esp = %08lx\n", t->eip, t->esp);
 
-                        printk("eax = %08lx, ebx = %08lx, ecx = %08lx, edx = %08lx\n",
+                        printk(KERN_EMERG "eax = %08lx, ebx = %08lx, ecx = %08lx, edx = %08lx\n",
                                 t->eax, t->ebx, t->ecx, t->edx);
-                        printk("esi = %08lx, edi = %08lx\n",
+                        printk(KERN_EMERG "esi = %08lx, edi = %08lx\n",
                                 t->esi, t->edi);
                 }
         }
@@ -63,6 +63,7 @@ struct tss_struct doublefault_tss __cacheline_aligned = {
                 .cs             = __KERNEL_CS,
                 .ss             = __KERNEL_DS,
                 .ds             = __USER_DS,
+                .fs             = __KERNEL_PERCPU,
 
                 .__cr3          = __pa(swapper_pg_dir)
         }