[PATCH] x86_64: Dump leftover backtrace entries when dwarf2 unwinder got stuck
[deliverable/linux.git] / arch / x86_64 / kernel / traps.c
index 08f24359bfc157eb94100074c80ac20eb771cc9d..f7a9d1421078648304f243347bc3f6238428488b 100644 (file)
@@ -12,7 +12,6 @@
  * 'Traps.c' handles hardware traps and faults after we have saved some
  * state in 'entry.S'.
  */
-#include <linux/config.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
@@ -70,19 +69,20 @@ asmlinkage void machine_check(void);
 asmlinkage void spurious_interrupt_bug(void);
 
 ATOMIC_NOTIFIER_HEAD(die_chain);
+EXPORT_SYMBOL(die_chain);
 
 int register_die_notifier(struct notifier_block *nb)
 {
        vmalloc_sync_all();
        return atomic_notifier_chain_register(&die_chain, nb);
 }
-EXPORT_SYMBOL(register_die_notifier);
+EXPORT_SYMBOL(register_die_notifier); /* used modular by kdb */
 
 int unregister_die_notifier(struct notifier_block *nb)
 {
        return atomic_notifier_chain_unregister(&die_chain, nb);
 }
-EXPORT_SYMBOL(unregister_die_notifier);
+EXPORT_SYMBOL(unregister_die_notifier); /* used modular by kdb */
 
 static inline void conditional_sti(struct pt_regs *regs)
 {
@@ -110,28 +110,31 @@ static int kstack_depth_to_print = 12;
 static int call_trace = 1;
 
 #ifdef CONFIG_KALLSYMS
-#include <linux/kallsyms.h> 
-int printk_address(unsigned long address)
-{ 
+# include <linux/kallsyms.h>
+void printk_address(unsigned long address)
+{
        unsigned long offset = 0, symsize;
        const char *symname;
        char *modname;
-       char *delim = ":"; 
+       char *delim = ":";
        char namebuf[128];
 
-       symname = kallsyms_lookup(address, &symsize, &offset, &modname, namebuf); 
-       if (!symname) 
-               return printk("[<%016lx>]", address);
-       if (!modname) 
+       symname = kallsyms_lookup(address, &symsize, &offset,
+                                       &modname, namebuf);
+       if (!symname) {
+               printk(" [<%016lx>]\n", address);
+               return;
+       }
+       if (!modname)
                modname = delim = "";           
-        return printk("<%016lx>{%s%s%s%s%+ld}",
-                     address, delim, modname, delim, symname, offset); 
-} 
+       printk(" [<%016lx>] %s%s%s%s+0x%lx/0x%lx\n",
+               address, delim, modname, delim, symname, offset, symsize);
+}
 #else
-int printk_address(unsigned long address)
-{ 
-       return printk("[<%016lx>]", address);
-} 
+void printk_address(unsigned long address)
+{
+       printk(" [<%016lx>]\n", address);
+}
 #endif
 
 static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
@@ -149,10 +152,22 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
        };
        unsigned k;
 
+       /*
+        * Iterate over all exception stacks, and figure out whether
+        * 'stack' is in one of them:
+        */
        for (k = 0; k < N_EXCEPTION_STACKS; k++) {
                unsigned long end;
 
+               /*
+                * set 'end' to the end of the exception stack.
+                */
                switch (k + 1) {
+               /*
+                * TODO: this block is not needed i think, because
+                * setup64.c:cpu_init() sets up t->ist[DEBUG_STACK]
+                * properly too.
+                */
 #if DEBUG_STKSZ > EXCEPTION_STKSZ
                case DEBUG_STACK:
                        end = cpu_pda(cpu)->debugstack + DEBUG_STKSZ;
@@ -162,19 +177,43 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
                        end = per_cpu(init_tss, cpu).ist[k];
                        break;
                }
+               /*
+                * Is 'stack' above this exception frame's end?
+                * If yes then skip to the next frame.
+                */
                if (stack >= end)
                        continue;
+               /*
+                * Is 'stack' above this exception frame's start address?
+                * If yes then we found the right frame.
+                */
                if (stack >= end - EXCEPTION_STKSZ) {
+                       /*
+                        * Make sure we only iterate through an exception
+                        * stack once. If it comes up for the second time
+                        * then there's something wrong going on - just
+                        * break out and return NULL:
+                        */
                        if (*usedp & (1U << k))
                                break;
                        *usedp |= 1U << k;
                        *idp = ids[k];
                        return (unsigned long *)end;
                }
+               /*
+                * If this is a debug stack, and if it has a larger size than
+                * the usual exception stacks, then 'stack' might still
+                * be within the lower portion of the debug stack:
+                */
 #if DEBUG_STKSZ > EXCEPTION_STKSZ
                if (k == DEBUG_STACK - 1 && stack >= end - DEBUG_STKSZ) {
                        unsigned j = N_EXCEPTION_STACKS - 1;
 
+                       /*
+                        * Black magic. A large debug stack is composed of
+                        * multiple exception stack entries, which we
+                        * iterate through now. Dont look:
+                        */
                        do {
                                ++j;
                                end -= EXCEPTION_STKSZ;
@@ -193,20 +232,14 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
 
 static int show_trace_unwind(struct unwind_frame_info *info, void *context)
 {
-       int i = 11, n = 0;
+       int n = 0;
 
        while (unwind(info) == 0 && UNW_PC(info)) {
-               ++n;
-               if (i > 50) {
-                       printk("\n       ");
-                       i = 7;
-               } else
-                       i += printk(" ");
-               i += printk_address(UNW_PC(info));
+               n++;
+               printk_address(UNW_PC(info));
                if (arch_unw_user_mode(info))
                        break;
        }
-       printk("\n");
        return n;
 }
 
@@ -221,10 +254,9 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
 {
        const unsigned cpu = safe_smp_processor_id();
        unsigned long *irqstack_end = (unsigned long *)cpu_pda(cpu)->irqstackptr;
-       int i = 11;
        unsigned used = 0;
 
-       printk("\nCall Trace:");
+       printk("\nCall Trace:\n");
 
        if (!tsk)
                tsk = current;
@@ -242,24 +274,32 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
                        if (unwind_init_blocked(&info, tsk) == 0)
                                unw_ret = show_trace_unwind(&info, NULL);
                }
-               if (unw_ret > 0) {
-                       if (call_trace > 0)
+               if (unw_ret > 0 && !arch_unw_user_mode(&info)) {
+#ifdef CONFIG_STACK_UNWIND
+                       unsigned long rip = info.regs.rip;
+                       print_symbol("DWARF2 unwinder stuck at %s\n", rip);
+                       if (call_trace == 1) {
+                               printk("Leftover inexact backtrace:\n");
+                               stack = (unsigned long *)info.regs.rsp;
+                       } else if (call_trace > 1)
                                return;
-                       printk("Legacy call trace:");
-                       i = 18;
+                       else
+                               printk("Full inexact backtrace again:\n");
+#else
+                       printk("Inexact backtrace:\n");
+#endif
                }
        }
 
+       /*
+        * Print function call entries within a stack. 'cond' is the
+        * "end of stackframe" condition, that the 'stack++'
+        * iteration will eventually trigger.
+        */
 #define HANDLE_STACK(cond) \
        do while (cond) { \
                unsigned long addr = *stack++; \
                if (kernel_text_address(addr)) { \
-                       if (i > 50) { \
-                               printk("\n       "); \
-                               i = 0; \
-                       } \
-                       else \
-                               i += printk(" "); \
                        /* \
                         * If the address is either in the text segment of the \
                         * kernel, or in the region which contains vmalloc'ed \
@@ -268,20 +308,30 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
                         * down the cause of the crash will be able to figure \
                         * out the call path that was taken. \
                         */ \
-                       i += printk_address(addr); \
+                       printk_address(addr); \
                } \
        } while (0)
 
-       for(; ; ) {
+       /*
+        * Print function call entries in all stacks, starting at the
+        * current stack address. If the stacks consist of nested
+        * exceptions
+        */
+       for ( ; ; ) {
                const char *id;
                unsigned long *estack_end;
                estack_end = in_exception_stack(cpu, (unsigned long)stack,
                                                &used, &id);
 
                if (estack_end) {
-                       i += printk(" <%s>", id);
+                       printk(" <%s>", id);
                        HANDLE_STACK (stack < estack_end);
-                       i += printk(" <EOE>");
+                       printk(" <EOE>");
+                       /*
+                        * We link to the next stack via the
+                        * second-to-last pointer (index -2 to end) in the
+                        * exception stack:
+                        */
                        stack = (unsigned long *) estack_end[-2];
                        continue;
                }
@@ -291,19 +341,28 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
                                (IRQSTACKSIZE - 64) / sizeof(*irqstack);
 
                        if (stack >= irqstack && stack < irqstack_end) {
-                               i += printk(" <IRQ>");
+                               printk(" <IRQ>");
                                HANDLE_STACK (stack < irqstack_end);
+                               /*
+                                * We link to the next stack (which would be
+                                * the process stack normally) the last
+                                * pointer (index -1 to end) in the IRQ stack:
+                                */
                                stack = (unsigned long *) (irqstack_end[-1]);
                                irqstack_end = NULL;
-                               i += printk(" <EOI>");
+                               printk(" <EOI>");
                                continue;
                        }
                }
                break;
        }
 
+       /*
+        * This prints the process stack:
+        */
        HANDLE_STACK (((long) stack & (THREAD_SIZE-1)) != 0);
 #undef HANDLE_STACK
+
        printk("\n");
 }
 
@@ -337,8 +396,8 @@ static void _show_stack(struct task_struct *tsk, struct pt_regs *regs, unsigned
                        break;
                }
                if (i && ((i % 4) == 0))
-                       printk("\n       ");
-               printk("%016lx ", *stack++);
+                       printk("\n");
+               printk(" %016lx", *stack++);
                touch_nmi_watchdog();
        }
        show_trace(tsk, regs, rsp);
@@ -431,6 +490,7 @@ void out_of_line_bug(void)
 { 
        BUG(); 
 } 
+EXPORT_SYMBOL(out_of_line_bug);
 #endif
 
 static DEFINE_SPINLOCK(die_lock);
@@ -1066,8 +1126,10 @@ static int __init call_trace_setup(char *s)
                call_trace = -1;
        else if (strcmp(s, "both") == 0)
                call_trace = 0;
-       else if (strcmp(s, "new") == 0)
+       else if (strcmp(s, "newfallback") == 0)
                call_trace = 1;
+       else if (strcmp(s, "new") == 0)
+               call_trace = 2;
        return 1;
 }
 __setup("call_trace=", call_trace_setup);
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