Messages in this thread | | | Date | Tue, 07 Aug 2012 17:38:45 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH 0/2] ptrace: DEBUGCTLMSR_BTF fixes |
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On 08/07/2012 05:15 PM, Oleg Nesterov wrote: >> So I think __switch_to_extra() should set the bit before putting the >> task on the CPU. > > Why?
Pardon me? __switch_to_extra() enables BTF before putting the task on CPU. This is fine. I was trying to say that there is no need to touch the debug register in debugger's context since __switch_to_extra() does it.
>> If this bit is enabled on the wrong CPU then in will >> remain set forever if single steeping has not been / will not be >> enabled. > > I don't follow, could you explain in details?
The SMP case where the debugger runs on CPU0 and tracee on CPU1. Without your "current != child" check the enable_block_step() enables block stepping on CPU0 and switch_to_extra() on CPU1.
> Just in case, X86_EFLAGS_TF sits in task_pt_regs(next), it has no > effect until the task returns to usermode. We only need to ensure > DEBUGCTLMSR_BTF was set/cleared correctly when it actually returns.
Exactly. And __switch_to_extra() is perfect for the job (if we ignore uprobes for a moment).
> Oleg.
Sebastian
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