Messages in this thread | | | Date | Mon, 21 Nov 2016 15:37:16 +0100 | From | Peter Zijlstra <> | Subject | Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage! |
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On Mon, Nov 21, 2016 at 09:15:43AM -0500, Steven Rostedt wrote: > On Mon, 21 Nov 2016 13:58:30 +0100 > Peter Zijlstra <peterz@infradead.org> wrote: > > > On Mon, Nov 21, 2016 at 10:34:25AM +0100, Jiri Olsa wrote: > > > > > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > > > index 0888a879120f..d6c6aa80675f 100644 > > > > --- a/arch/x86/kernel/process.c > > > > +++ b/arch/x86/kernel/process.c > > > > @@ -357,7 +357,7 @@ static void amd_e400_idle(void) > > > > if (!amd_e400_c1e_detected) { > > > > u32 lo, hi; > > > > > > > > - rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi); > > > > + RCU_NONIDLE(rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi)); > > > > > > > > if (lo & K8_INTP_C1E_ACTIVE_MASK) { > > > > amd_e400_c1e_detected = true; > > > > OK, so while looking at this again, I don't like this ether :/ > > > > Problem with this one is that it always adds the RCU fiddling overhead, > > even when we're not tracing. > > > > I could do an rdmsr_notrace() for this one, dunno if its important. > > But that would neglect the point of tracing rdmsr. What about: > > /* tracepoints require RCU enabled */ > if (trace_read_msr_enabled()) > RCU_NONIDLE(rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi)); > else > rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
Yeah, but this one does a printk() when it hits the contidion it checks for, so not tracing it would be fine I think.
Also, Boris, why do we need to redo that rdmsr until we see that bit set? Can't we simply do the rdmsr once and then be done with it?
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