Commit ea424055 authored by Jan Beulich's avatar Jan Beulich Committed by Linus Torvalds
Browse files

[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: default avatarJan Beulich <jbeulich@novell.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 61171b8d

arch/i386/kernel/traps.c

+16 −11
Original line number Diff line number Diff line
@@ -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

		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 (call_trace == 1) {

				if (UNW_SP(&info) >= PAGE_OFFSET) {

					printk("Leftover inexact backtrace:\n");

				if (UNW_SP(&info))

					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

arch/x86_64/kernel/traps.c

+17 −11
Original line number Diff line number Diff line
@@ -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) {

		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 *)info.regs.rsp;

			} else if (call_trace > 1)

					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

include/asm-i386/unwind.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

{

include/asm-x86_64/unwind.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

{

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