Messages in this thread | | | Date | Wed, 01 Aug 2012 15:32:37 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: Q: user_enable_single_step() && update_debugctlmsr() |
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On 08/01/2012 03:01 PM, Oleg Nesterov wrote: > Lets ignore uprobes which needs the changes anyway. This is > only used by ptrace and the task is stopped. So, unless I missed > something obvious, this update_debugctlmsr() is simply unneeded, > __switch_to/__switch_to_xtra should notice _TIF_BLOCKSTEP and do > update_debugctlmsr(DEBUGCTLMSR_BTF).
It looks like it unless a processes ptraces itself (which does not make much sense anyway).
> But, worse, isn't it wrong? Suppose that debugger switches to > another TIF_SINGLESTEP&& !TIF_BLOCKSTEP task, in this case > we "leak" DEBUGCTLMSR_BTF, no?
__switch_to_xtra() should notice the difference in the TIF_BLOCKSTEP flag and disable it.
> IOW, it seems to me we could safely remove update_debugctlmsr() > arch/x86/kernel/step.c. However, if we want to re-use this code > in uprobes, then we probably need to add "if (child == current)". It looks that way.
> > Or I am totally confused. Help! > > Oleg.
Sebastian
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