linux-kernel - Re: [PATCH] perf/x86/intel: Make cpuc allocations consistent

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Date:   Fri, 15 Mar 2019 09:14:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] perf/x86/intel: Make cpuc allocations consistent

On Thu, Mar 14, 2019 at 02:10:14PM -0700, Guenter Roeck wrote:
> On Tue, Mar 05, 2019 at 10:23:15PM +0100, Peter Zijlstra (Intel) wrote:
> > The cpuc data structure allocation is different between fake and real
> > cpuc's; use the same code to init/free both.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> With allmodconfig-CONFIG_CPU_SUP_INTEL, this patch results in:
> 
> In file included from arch/x86/events/amd/core.c:8:0:
> arch/x86/events/amd/../perf_event.h:1036:45: warning: ‘struct cpu_hw_event’ declared inside parameter list will not be visible outside of this definition or declaration
>  static inline int intel_cpuc_prepare(struct cpu_hw_event *cpuc, int cpu)
>                                              ^~~~~~~~~~~~
> arch/x86/events/amd/../perf_event.h:1041:45: warning: ‘struct cpu_hw_event’ declared inside parameter list will not be visible outside of this definition or declaration
>  static inline void intel_cpuc_finish(struct cpu_hw_event *cpuc)
>                                              ^~~~~~~~~~~~
> 
> With -Werror, this is fatal, and I think it may be buggy (should it be
> cpu_hw_events) ?

Yep it should be. Won't result in a bug though, an unused pointer is an
unused poiner, no matter what known or unknown type it points to.

> The patch has been applied to stable releases. Any idea, anyone, why
> this is the case ? It doesn't look like a bug fix to me, and reverting
> it from v4.14.106 didn't seem to have a negative impact.

Reverting just this one patch will make your kernel go boom when you run
on a skylake or more recent Intel cpu, have updated your microcode and
do:

  echo 0 > /sys/bus/event_source/devices/cpu/allow_tsx_force_abort

And then try and create perf events. See also commit:

  400816f60c54 ("perf/x86/intel: Implement support for TSX Force Abort")

---
Subject: perf/x86: Fixup typo in stub functions

Guenter reported a build warning for CONFIG_CPU_SUP_INTEL=n. While
harmless (an unsed pointer is an unused pointer, no matter the type) it
needs fixing.

Reported-by: Guenter Roeck <linux@...ck-us.net>
Fixes: d01b1f96a82e ("perf/x86/intel: Make cpuc allocations consistent")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/events/perf_event.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index b04ae6c8775e..a75955741c50 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1033,12 +1033,12 @@ static inline int intel_pmu_init(void)
 	return 0;
 }
 
-static inline int intel_cpuc_prepare(struct cpu_hw_event *cpuc, int cpu)
+static inline int intel_cpuc_prepare(struct cpu_hw_events *cpuc, int cpu)
 {
 	return 0;
 }
 
-static inline void intel_cpuc_finish(struct cpu_hw_event *cpuc)
+static inline void intel_cpuc_finish(struct cpu_hw_events *cpuc)
 {
 }