[PATCH] x86: Make backtracer fallback logic more bullet-proof

The unwinder fallback logic still had potential for falling through to
the legacy stack trace code without printing an indication (at once
serving as a separator) of this.

Further, the stack pointer retrieval for the fallback should be as
restrictive as possible (in order to avoid having the legacy stack
tracer try to access invalid memory). The patch tightens that, but
this could certainly be further improved.

Also making the call_trace command line option now conditional upon
CONFIG_STACK_UNWIND (as it's meaningless otherwise).

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index 82e0fd02af1c5b7dcaf92a98c76899684e77b85b..7e9edafffd8ad8cbac338870357f2a3b2478238b 100644 (file)
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -92,7 +92,11 @@ asmlinkage void spurious_interrupt_bug(void);
 asmlinkage void machine_check(void);
 
 static int kstack_depth_to_print = 24;
+#ifdef CONFIG_STACK_UNWIND
 static int call_trace = 1;
+#else
+#define call_trace (-1)
+#endif
 ATOMIC_NOTIFIER_HEAD(i386die_chain);
 
 int register_die_notifier(struct notifier_block *nb)
@@ -187,22 +191,21 @@ static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
                        if (unwind_init_blocked(&info, task) == 0)
                                unw_ret = show_trace_unwind(&info, log_lvl);
                }
-               if (unw_ret > 0 && !arch_unw_user_mode(&info)) {
-#ifdef CONFIG_STACK_UNWIND
-                       print_symbol("DWARF2 unwinder stuck at %s\n",
-                                    UNW_PC(&info));
-                       if (call_trace == 1) {
-                               printk("Leftover inexact backtrace:\n");
-                               if (UNW_SP(&info))
+               if (unw_ret > 0) {
+                       if (call_trace == 1 && !arch_unw_user_mode(&info)) {
+                               print_symbol("DWARF2 unwinder stuck at %s\n",
+                                            UNW_PC(&info));
+                               if (UNW_SP(&info) >= PAGE_OFFSET) {
+                                       printk("Leftover inexact backtrace:\n");
                                        stack = (void *)UNW_SP(&info);
-                       } else if (call_trace > 1)
+                               } else
+                                       printk("Full inexact backtrace again:\n");
+                       } else if (call_trace >= 1)
                                return;
                        else
                                printk("Full inexact backtrace again:\n");
-#else
+               } else
                        printk("Inexact backtrace:\n");
-#endif
-               }
        }
 
        if (task == current) {
@@ -1241,6 +1244,7 @@ static int __init kstack_setup(char *s)
 }
 __setup("kstack=", kstack_setup);
 
+#ifdef CONFIG_STACK_UNWIND
 static int __init call_trace_setup(char *s)
 {
        if (strcmp(s, "old") == 0)
@@ -1254,3 +1258,4 @@ static int __init call_trace_setup(char *s)
        return 1;
 }
 __setup("call_trace=", call_trace_setup);
+#endif

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 14052f08981498a2ef13c0b2feaab12498ca07e3..5e00af54af653aa3fc7be766f58db5c6648b1977 100644 (file)
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -107,7 +107,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 }
 
 static int kstack_depth_to_print = 12;
+#ifdef CONFIG_STACK_UNWIND
 static int call_trace = 1;
+#else
+#define call_trace (-1)
+#endif
 
 #ifdef CONFIG_KALLSYMS
 # include <linux/kallsyms.h>
@@ -274,21 +278,21 @@ 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 && !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)
+               if (unw_ret > 0) {
+                       if (call_trace == 1 && !arch_unw_user_mode(&info)) {
+                               print_symbol("DWARF2 unwinder stuck at %s\n",
+                                            UNW_PC(&info));
+                               if ((long)UNW_SP(&info) < 0) {
+                                       printk("Leftover inexact backtrace:\n");
+                                       stack = (unsigned long *)UNW_SP(&info);
+                               } else
+                                       printk("Full inexact backtrace again:\n");
+                       } else if (call_trace >= 1)
                                return;
                        else
                                printk("Full inexact backtrace again:\n");
-#else
+               } else
                        printk("Inexact backtrace:\n");
-#endif
-               }
        }
 
        /*
@@ -1120,6 +1124,7 @@ static int __init kstack_setup(char *s)
 }
 __setup("kstack=", kstack_setup);
 
+#ifdef CONFIG_STACK_UNWIND
 static int __init call_trace_setup(char *s)
 {
        if (strcmp(s, "old") == 0)
@@ -1133,3 +1138,4 @@ static int __init call_trace_setup(char *s)
        return 1;
 }
 __setup("call_trace=", call_trace_setup);
+#endif

diff --git a/include/asm-i386/unwind.h b/include/asm-i386/unwind.h
index 69f0f1df67220edd0bc7bfe0b2148c6038b86e05..4c1a0b968569ef64844d1ad5d159ce7b44141249 100644 (file)
--- a/include/asm-i386/unwind.h
+++ b/include/asm-i386/unwind.h
@@ -87,6 +87,7 @@ static inline int arch_unw_user_mode(const struct unwind_frame_info *info)
 #else
 
 #define UNW_PC(frame) ((void)(frame), 0)
+#define UNW_SP(frame) ((void)(frame), 0)
 
 static inline int arch_unw_user_mode(const void *info)
 {

diff --git a/include/asm-x86_64/unwind.h b/include/asm-x86_64/unwind.h
index f3e7124effe3102a69e7fb0b5e81ae78b0092d76..1f6e9bfb569e7ef6f645af572ee2a030c21f1a83 100644 (file)
--- a/include/asm-x86_64/unwind.h
+++ b/include/asm-x86_64/unwind.h
@@ -95,6 +95,7 @@ static inline int arch_unw_user_mode(const struct unwind_frame_info *info)
 #else
 
 #define UNW_PC(frame) ((void)(frame), 0)
+#define UNW_SP(frame) ((void)(frame), 0)
 
 static inline int arch_unw_user_mode(const void *info)
 {