(2012/02/02 6:06), Steven Rostedt wrote:
> Preemption must be disabled before enabling interrupts in do_trap
> on x86_64 because the stack in use for int3 and debug is a per CPU
> stack set by th IST. But 32bit does not have an IST and the stack
> still belongs to the current task and there is no problem in scheduling
> out the task.
>
> Keep preemption enabled on X86_32 when enabling interrupts for
> do_trap().
>
> The name of the function is changed from preempt_conditional_sti/cli()
> to conditional_sti/cli_ist(), to annotate that this function is used
> when the stack is on the IST.
>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Thanks!
>
> Index: linux-rt.git/arch/x86/kernel/traps.c
> ===================================================================
> --- linux-rt.git.orig/arch/x86/kernel/traps.c
> +++ linux-rt.git/arch/x86/kernel/traps.c
> @@ -87,9 +87,21 @@ static inline void conditional_sti(struc
> local_irq_enable();
> }
>
> -static inline void preempt_conditional_sti(struct pt_regs *regs)
> +static inline void conditional_sti_ist(struct pt_regs *regs)
> {
> +#ifdef CONFIG_X86_64
> + /*
> + * X86_64 uses a per CPU stack on the IST for certain traps
> + * like int3. The task can not be preempted when using one
> + * of these stacks, thus preemption must be disabled, otherwise
> + * the stack can be corrupted if the task is scheduled out,
> + * and another task comes in and uses this stack.
> + *
> + * On x86_32 the task keeps its own stack and it is OK if the
> + * task schedules out.
> + */
> inc_preempt_count();
> +#endif
> if (regs->flags & X86_EFLAGS_IF)
> local_irq_enable();
> }
> @@ -100,11 +112,13 @@ static inline void conditional_cli(struc
> local_irq_disable();
> }
>
> -static inline void preempt_conditional_cli(struct pt_regs *regs)
> +static inline void conditional_cli_ist(struct pt_regs *regs)
> {
> if (regs->flags & X86_EFLAGS_IF)
> local_irq_disable();
> +#ifdef CONFIG_X86_64
> dec_preempt_count();
> +#endif
> }
>
> static void __kprobes
> @@ -222,9 +236,9 @@ dotraplinkage void do_stack_segment(stru
> if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
> 12, SIGBUS) == NOTIFY_STOP)
> return;
> - preempt_conditional_sti(regs);
> + conditional_sti_ist(regs);
> do_trap(12, SIGBUS, "stack segment", regs, error_code, NULL);
> - preempt_conditional_cli(regs);
> + conditional_cli_ist(regs);
> }
>
> dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
> @@ -316,9 +330,9 @@ dotraplinkage void __kprobes do_int3(str
> return;
> #endif
>
> - preempt_conditional_sti(regs);
> + conditional_sti_ist(regs);
> do_trap(3, SIGTRAP, "int3", regs, error_code, NULL);
> - preempt_conditional_cli(regs);
> + conditional_cli_ist(regs);
> }
>
> #ifdef CONFIG_X86_64
> @@ -412,12 +426,12 @@ dotraplinkage void __kprobes do_debug(st
> return;
>
> /* It's safe to allow irq's after DR6 has been saved */
> - preempt_conditional_sti(regs);
> + conditional_sti_ist(regs);
>
> if (regs->flags & X86_VM_MASK) {
> handle_vm86_trap((struct kernel_vm86_regs *) regs,
> error_code, 1);
> - preempt_conditional_cli(regs);
> + conditional_cli_ist(regs);
> return;
> }
>
> @@ -436,7 +450,7 @@ dotraplinkage void __kprobes do_debug(st
> si_code = get_si_code(tsk->thread.debugreg6);
> if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
> send_sigtrap(tsk, regs, error_code, si_code);
> - preempt_conditional_cli(regs);
> + conditional_cli_ist(regs);
>
> return;
> }
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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