Messages in this thread | | | Date | Wed, 1 Aug 2012 17:14:42 +0200 | From | Oleg Nesterov <> | Subject | Re: Q: user_enable_single_step() && update_debugctlmsr() |
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On 08/01, Sebastian Andrzej Siewior wrote: > > On 08/01/2012 05:01 PM, Oleg Nesterov wrote: >> On 08/01, Sebastian Andrzej Siewior wrote: >>> So a patch like >>> --- a/arch/x86/kernel/step.c >>> +++ b/arch/x86/kernel/step.c >>> @@ -173,8 +173,8 @@ static void enable_step(struct task_struct *child, >>> bool block) >>> unsigned long debugctl = get_debugctlmsr(); >>> >>> debugctl |= DEBUGCTLMSR_BTF; >>> - update_debugctlmsr(debugctl); >>> set_tsk_thread_flag(child, TIF_BLOCKSTEP); >>> + update_debugctlmsr(debugctl); >>> } else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) { >>> unsigned long debugctl = get_debugctlmsr(); >>> >>> should fix the race >> >> No, I don't think it can fix something ;) or make any difference. > > Why? You _first_ set the task flag
Yes, and this task is "child".
> followed by the CPU register. Now > switch_to() would see the bit set and act.
child sleeps and doesn't participate in switch_to(). Debugger and another (unrelated) task do.
Oleg.
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