On Thu, Aug 09, 2007 at 07:35:39PM -0400, Chuck Ebbert wrote:
> On 08/09/2007 07:16 PM, Andi Kleen wrote:
> >
> > I tested it. Even on a box without spin lock debugging I get a hard
> > hang after
> >
> > double fault, gdt at c1404000 [255 bytes]
> >
> > even though it should have printed the registers.
> > So it looks like there is more broken in the DF handler than just
> > this.
>
> Looks like it just fails the ptr_ok() test:
>
> #define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + 0x1000000)
>
> page_offset c0000000
> + 1000000
>
> < c1404000
>
> What should that be changed to, or is there some easier way to test that?
This is the patch i came up with in the end. Passes testing.
I also fixed some more minor things.
Fix double fault handler
From: Chuck Ebbert <[email protected]>
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 <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
arch/i386/kernel/doublefault.c | 1 +
1 file changed, 1 insertion(+)
Index: linux/arch/i386/kernel/doublefault.c
===================================================================
--- linux.orig/arch/i386/kernel/doublefault.c
+++ linux/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)
{
@@ -23,7 +23,7 @@ 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;
@@ -35,11 +35,11 @@ static void doublefault_fn(void)
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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