From f8988175fd70874d1fb3712b1c5d3bfc6d455202 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 30 May 2012 11:47:00 -0400 Subject: x86: Allow nesting of the debug stack IDT setting When the NMI handler runs, it checks if it preempted a debug handler and if that handler is using the debug stack. If it is, it changes the IDT table not to update the stack, otherwise it will reset the debug stack and corrupt the debug handler it preempted. Now that ftrace uses breakpoints to change functions from nops to callers, many more places may hit a breakpoint. Unfortunately this includes some of the calls that lockdep performs. Which causes issues with the debug stack. It too needs to change the debug stack before tracing (if called from the debug handler). Allow the debug_stack_set_zero() and debug_stack_reset() to be nested so that the debug handlers can take advantage of them too. [ Used this_cpu_*() over __get_cpu_var() as suggested by H. Peter Anvin ] Signed-off-by: Steven Rostedt --- arch/x86/kernel/cpu/common.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 82f29e70d05..6b9333b429b 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1101,14 +1101,20 @@ int is_debug_stack(unsigned long addr) addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ)); } +static DEFINE_PER_CPU(u32, debug_stack_use_ctr); + void debug_stack_set_zero(void) { + this_cpu_inc(debug_stack_use_ctr); load_idt((const struct desc_ptr *)&nmi_idt_descr); } void debug_stack_reset(void) { - load_idt((const struct desc_ptr *)&idt_descr); + if (WARN_ON(!this_cpu_read(debug_stack_use_ctr))) + return; + if (this_cpu_dec_return(debug_stack_use_ctr) == 0) + load_idt((const struct desc_ptr *)&idt_descr); } #else /* CONFIG_X86_64 */ -- cgit v1.2.3-70-g09d2