On 08/07, Sebastian Andrzej Siewior wrote: > > 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.
And this is what the changelog says and the patch does? Confused. >>> 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. Sure, and after the patch it doesn't touch BTF if current != child. >> 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). Exactly. Ah. I guess I simply misunderstood your original email. Sorry. Somehow I thought you think that __switch_to_extra() needs fixes too. Sorry for noise. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
