Messages in this thread Patch in this message | | | Subject | [PATCH] tracing: generate RCU warnings even when tracepoints are disabled | From | Dave Hansen <> | Date | Thu, 07 Aug 2014 10:52:04 -0700 |
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From: Dave Hansen <dave.hansen@linux.intel.com>
Dave Jones reported seeing a bug from one of my TLB tracepoints:
http://lkml.kernel.org/r/20140806181801.GA4605@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.hansen@linux.intel.com> Cc: Dave Jones <davej@redhat.com>, Cc: paulmck@linux.vnet.ibm.com Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ingo Molnar <mingo@redhat.com>
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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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