Hi Linus,
2 weeks ago I sent you a bugfix for show_registers()
[arch/i386/kernel/traps.c, used by die() to print the back trace]:
show_registers() locks up on SMP and prints a mangled oops report on UP if
the EIP value got corrupted, eg because a function pointer was
uninitialized [eg. gdth-scsi driver], or because a module was unloaded.
AFAICS there a 3 options to prevent this crash:
* walk the page tables. Ugly, and you dismissed that patch last year ;)
* walk the module list. IMHO even worse than the page table walk.
Andi Keen uses a similar approach in his kbacktrace patch.
* use __get_user(). I've implemented this approach in the attached patch.
Could you reconsider this patch, or do you have a better idea how to solve
the problem?
The patch is tested on i386 SMP (2.3.39) and 2.3.40-3 doesn't touch
traps.c
--
Manfred
<<<<<<<<<<<<<<<<<
--- 2.3/arch/i386/kernel/traps.c Tue Dec 14 18:20:08 1999
+++ build-2.3/arch/i386/kernel/traps.c Mon Jan 3 13:28:07 2000
@@ -124,19 +124,63 @@
/*
* These constants are for searching for possible module text
- * segments. VMALLOC_OFFSET comes from mm/vmalloc.c; MODULE_RANGE is
- * a guess of how much space is likely to be vmalloced.
+ * segments. MODULE_RANGE is a guess of how much space is likely
+ * to be vmalloced.
*/
-#define VMALLOC_OFFSET (8*1024*1024)
#define MODULE_RANGE (8*1024*1024)
+void show_stack(unsigned long * esp)
+{
+ unsigned long *stack, addr, module_start, module_end;
+ int i;
+
+ // debugging aid: "show_stack(NULL);" prints the full
+ // back trace.
+
+ if(esp==NULL)
+ esp=(unsigned long*)&esp;
+
+ stack = esp;
+ for(i=0; i < kstack_depth_to_print; i++) {
+ if (((long) stack & (THREAD_SIZE-1)) == 0)
+ break;
+ if (i && ((i % 8) == 0))
+ printk("\n ");
+ printk("%08lx ", *stack++);
+ }
+
+ printk("\nCall Trace: ");
+ stack = esp;
+ i = 1;
+ module_start = VMALLOC_START;
+ module_end = module_start + MODULE_RANGE;
+ while (((long) stack & (THREAD_SIZE-1)) != 0) {
+ addr = *stack++;
+ /*
+ * If the address is either in the text segment of the
+ * kernel, or in the region which contains vmalloc'ed
+ * memory, it *may* be the address of a calling
+ * routine; if so, print it so that someone tracing
+ * down the cause of the crash will be able to figure
+ * out the call path that was taken.
+ */
+ if (((addr >= (unsigned long) &_stext) &&
+ (addr <= (unsigned long) &_etext)) ||
+ ((addr >= module_start) && (addr <= module_end))) {
+ if (i && ((i % 8) == 0))
+ printk("\n ");
+ printk("[<%08lx>] ", addr);
+ i++;
+ }
+ }
+}
+
static void show_registers(struct pt_regs *regs)
{
int i;
int in_kernel = 1;
unsigned long esp;
unsigned short ss;
- unsigned long *stack, addr, module_start, module_end;
esp = (unsigned long) (1+regs);
ss = __KERNEL_DS;
@@ -160,43 +204,24 @@
* time of the fault..
*/
if (in_kernel) {
+
printk("\nStack: ");
- stack = (unsigned long *) esp;
- for(i=0; i < kstack_depth_to_print; i++) {
- if (((long) stack & 4095) == 0)
+ show_stack((unsigned long*)esp);
+
+ printk("\nCode: ");
+ if(regs->eip < PAGE_OFFSET)
+ goto bad;
+
+ for(i=0;i<20;i++)
+ {
+ unsigned char c;
+ if(__get_user(c, &((unsigned char*)regs->eip)[i])) {
+bad:
+ printk(" Bad EIP value.");
break;
- if (i && ((i % 8) == 0))
- printk("\n ");
- printk("%08lx ", *stack++);
- }
- printk("\nCall Trace: ");
- stack = (unsigned long *) esp;
- i = 1;
- module_start = PAGE_OFFSET + (max_mapnr << PAGE_SHIFT);
- module_start = ((module_start + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1));
- module_end = module_start + MODULE_RANGE;
- while (((long) stack & 4095) != 0) {
- addr = *stack++;
- /*
- * If the address is either in the text segment of the
- * kernel, or in the region which contains vmalloc'ed
- * memory, it *may* be the address of a calling
- * routine; if so, print it so that someone tracing
- * down the cause of the crash will be able to figure
- * out the call path that was taken.
- */
- if (((addr >= (unsigned long) &_stext) &&
- (addr <= (unsigned long) &_etext)) ||
- ((addr >= module_start) && (addr <= module_end))) {
- if (i && ((i % 8) == 0))
- printk("\n ");
- printk("[<%08lx>] ", addr);
- i++;
}
+ printk("%02x ", c);
}
- printk("\nCode: ");
- for(i=0;i<20;i++)
- printk("%02x ", ((unsigned char *)regs->eip)[i]);
}
printk("\n");
}
<<<<<<<<<<<<<<<<<
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