Messages in this thread Patch in this message | | | Date | Tue, 15 Aug 2006 12:53:22 +0200 | From | "Jan Beulich" <> | Subject | Re: backtracer stuck in apic_timer_interrupt |
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>Do you know why the backtracer gets stuck in apic_timer_interrupt? >Somehow it didn't manage to go over to the process stack, but it should >have.
No, I don't, I just verified that the annotations are correct (in that unwinds can pass this function). If you see this again, I'd need the raw stack dump to compare. However, while doing this I also saw a case where it wouldn't properly unwind (but one level up from apic_timer_interrupt), however in this case it was expectedly getting stuck because the interrupt had hit a procedure that already entered it epilogue, which gcc fails to annotate.
Further, while doing this, I found myself ending up with an unwound stack trace followed by a legacy one, but without any separator indicating so. Therefore I looked at the fallback logic you recently changed and found that it was still not quite right. Hence I created below patch (for both i386 and x86-64).
Jan
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>
--- linux-2.6.18-rc4/arch/i386/kernel/traps.c 2006-08-15 11:29:35.000000000 +0200 +++ 2.6.18-rc4-unwind-x86-fallback/arch/i386/kernel/traps.c 2006-08-15 10:52:43.000000000 +0200 @@ -92,7 +92,11 @@ asmlinkage void spurious_interrupt_bug(v 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 ta 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 return 1; } __setup("call_trace=", call_trace_setup); +#endif --- linux-2.6.18-rc4/arch/x86_64/kernel/traps.c 2006-08-15 11:29:41.000000000 +0200 +++ 2.6.18-rc4-unwind-x86-fallback/arch/x86_64/kernel/traps.c 2006-08-15 10:49:34.000000000 +0200 @@ -107,7 +107,11 @@ static inline void preempt_conditional_c } 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, 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 return 1; } __setup("call_trace=", call_trace_setup); +#endif --- linux-2.6.18-rc4/include/asm-i386/unwind.h 2006-08-15 11:30:00.000000000 +0200 +++ 2.6.18-rc4-unwind-x86-fallback/include/asm-i386/unwind.h 2006-08-15 09:36:19.000000000 +0200 @@ -87,6 +87,7 @@ static inline int arch_unw_user_mode(con #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) { --- linux-2.6.18-rc4/include/asm-x86_64/unwind.h 2006-08-15 11:30:02.000000000 +0200 +++ 2.6.18-rc4-unwind-x86-fallback/include/asm-x86_64/unwind.h 2006-08-15 09:36:19.000000000 +0200 @@ -95,6 +95,7 @@ static inline int arch_unw_user_mode(con #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) { - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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