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.
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