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Subject[patch 19/20] i386: Fix double fault handler

-stable review patch. If anyone has any objections, please let us know.

------------------
From: Chuck Ebbert <cebbert@redhat.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>


---
arch/i386/kernel/doublefault.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

--- 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 __cach
.cs = __KERNEL_CS,
.ss = __KERNEL_DS,
.ds = __USER_DS,
+ .fs = __KERNEL_PERCPU,

.__cr3 = __pa(swapper_pg_dir)
}
--
-
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