On Thu, Aug 07, 2014 at 10:52:04AM -0700, Dave Hansen wrote:
>
> From: Dave Hansen <dave.han...@linux.intel.com>
>
> Dave Jones reported seeing a bug from one of my TLB tracepoints:
>
> http://lkml.kernel.org/r/20140806181801.ga4...@redhat.com
>
> I've been running these patches for months and never saw this.
> But, a big chunk of my testing, especially with all the debugging
> enabled, was in a vm where intel_idle doesn't work. On the
> systems where I was using intel_idle, I never had lockdep enabled
> and this tracepoint on at the same time.
>
> This patch ensures that whenever we have lockdep available, we do
> _some_ RCU activity at the site of the tracepoint, despite
> whether the tracepoint's condition matches or even if the
> tracepoint itself is completely disabled. This is a bit of a
> hack, but it is pretty self-contained.
>
> I confirmed that with this patch plus lockdep I get the same
> splat as Dave Jones did, but without enabling the tracepoint
> explicitly.
>
> Signed-off-by: Dave Hansen <dave.han...@linux.intel.com>
> Cc: Dave Jones <da...@redhat.com>,
> Cc: paul...@linux.vnet.ibm.com
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Ingo Molnar <mi...@redhat.com>
Looks good to me, but I must defer to Steven on this one.
Thanx, Paul
> ---
>
> b/include/linux/tracepoint.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff -puN include/linux/tracepoint.h~easier-rcu-splat
> include/linux/tracepoint.h
> --- a/include/linux/tracepoint.h~easier-rcu-splat 2014-08-07
> 10:29:32.701217956 -0700
> +++ b/include/linux/tracepoint.h 2014-08-07 10:40:35.244627014 -0700
> @@ -157,6 +157,12 @@ extern void syscall_unregfunc(void);
> * Make sure the alignment of the structure in the __tracepoints section will
> * not add unwanted padding between the beginning of the section and the
> * structure. Force alignment to the same alignment as the section start.
> + *
> + * When lockdep is enabled, we make sure to always do the RCU portions of
> + * the tracepoint code, regardless of whether tracing is on or we match the
> + * condition. This lets us find RCU issues triggered with tracepoints even
> + * when this tracepoint is off. This code has no purpose other than poking
> + * RCU a bit.
> */
> #define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
> extern struct tracepoint __tracepoint_##name; \
> @@ -167,6 +173,11 @@ extern void syscall_unregfunc(void);
> TP_PROTO(data_proto), \
> TP_ARGS(data_args), \
> TP_CONDITION(cond),,); \
> + if (IS_ENABLED(CONFIG_LOCKDEP)) { \
> + rcu_read_lock_sched_notrace(); \
> + rcu_dereference_sched(__tracepoint_##name.funcs);\
> + rcu_read_unlock_sched_notrace(); \
> + } \
> } \
> __DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \
> PARAMS(cond), PARAMS(data_proto), PARAMS(data_args)) \
> _
>
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