From adb81348d16928a8f4856bc108706ebe2e77d911 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 3 Jul 2009 08:44:10 -0500 Subject: [PATCH] x86: Disable IST stacks for debug/int 3/stack fault for PREEMPT_RT commit 709f87cc806d3202e38ced8bfd8bdf3ff1f9929b in tip. Normally the x86-64 trap handlers for debug/int 3/stack fault run on a special interrupt stack to make them more robust when dealing with kernel code. The PREEMPT_RT kernel can sleep in locks even while allocating GFP_ATOMIC memory. When one of these trap handlers needs to send real time signals for ptrace it allocates memory and could then try to to schedule. But it is not allowed to schedule on a IST stack. This can cause warnings and hangs. This patch disables the IST stacks for these handlers for PREEMPT_RT kernel. Instead let them run on the normal process stack. The kernel only really needs the ISTs here to make kernel debuggers more robust in case someone sets a break point somewhere where the stack is invalid. But there are no kernel debuggers in the standard kernel that do this. It also means kprobes cannot be set in situations with invalid stack; but that sounds like a reasonable restriction. The stack fault change could minimally impact oops quality, but not very much because stack faults are fairly rare. A better solution would be to use similar logic as the NMI "paranoid" path: check if signal is for user space, if yes go back to entry.S, switch stack, call sync_regs, then do the signal sending etc. But this patch is much simpler and should work too with minimal impact. Signed-off-by: Andi Kleen Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Signed-off-by: Paul Gortmaker --- arch/x86/include/asm/page_64_types.h | 21 +++++++++++++++------ arch/x86/kernel/cpu/common.c | 2 ++ arch/x86/kernel/dumpstack_64.c | 4 ++++ 3 files changed, 21 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h index 7639dbf..0ec050a 100644 --- a/arch/x86/include/asm/page_64_types.h +++ b/arch/x86/include/asm/page_64_types.h @@ -14,12 +14,21 @@ #define IRQ_STACK_ORDER 2 #define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER) -#define STACKFAULT_STACK 1 -#define DOUBLEFAULT_STACK 2 -#define NMI_STACK 3 -#define DEBUG_STACK 4 -#define MCE_STACK 5 -#define N_EXCEPTION_STACKS 5 /* hw limit: 7 */ +#ifdef CONFIG_PREEMPT_RT +# define STACKFAULT_STACK 0 +# define DOUBLEFAULT_STACK 1 +# define NMI_STACK 2 +# define DEBUG_STACK 0 +# define MCE_STACK 3 +# define N_EXCEPTION_STACKS 3 /* hw limit: 7 */ +#else +# define STACKFAULT_STACK 1 +# define DOUBLEFAULT_STACK 2 +# define NMI_STACK 3 +# define DEBUG_STACK 4 +# define MCE_STACK 5 +# define N_EXCEPTION_STACKS 5 /* hw limit: 7 */ +#endif #define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT) #define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1)) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 4868e4a..fae7a32 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1013,7 +1013,9 @@ DEFINE_PER_CPU(unsigned int, irq_count) = -1; */ static const unsigned int exception_stack_sizes[N_EXCEPTION_STACKS] = { [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STKSZ, +#if DEBUG_STACK > 0 [DEBUG_STACK - 1] = DEBUG_STKSZ +#endif }; static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index 272c9f1..6b61d69 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -22,10 +22,14 @@ (N_EXCEPTION_STACKS + DEBUG_STKSZ/EXCEPTION_STKSZ - 2) static char x86_stack_ids[][8] = { +#if DEBUG_STACK > 0 [ DEBUG_STACK-1 ] = "#DB", +#endif [ NMI_STACK-1 ] = "NMI", [ DOUBLEFAULT_STACK-1 ] = "#DF", +#if STACKFAULT_STACK > 0 [ STACKFAULT_STACK-1 ] = "#SS", +#endif [ MCE_STACK-1 ] = "#MC", #if DEBUG_STKSZ > EXCEPTION_STKSZ [ N_EXCEPTION_STACKS ... -- 1.7.0.4