Messages in this thread Patch in this message | | | Date | Fri, 10 Aug 2007 10:23:10 +0200 | From | Andi Kleen <> | Subject | Re: i386 doublefault handler is broken with CONFIG_DEBUG_SPINLOCK |
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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 <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>
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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