Hi Joel,
On Wed, May 23, 2018 at 06:21:55PM -0700, Joel Fernandes wrote:
From: "Joel Fernandes (Google)" joel@joelfernandes.org
This patch detaches the preemptirq tracepoints from the tracers and keeps it separate.
Advantages:
- Lockdep and irqsoff event can now run in parallel since they no longer
have their own calls.
- This unifies the usecase of adding hooks to an irqsoff and irqson
event, and a preemptoff and preempton event. 3 users of the events exist:
- Lockdep
- irqsoff and preemptoff tracers
- irqs and preempt trace events
The unification cleans up several ifdefs and makes the code in preempt tracer and irqsoff tracers simpler. It gets rid of all the horrific ifdeferry around PROVE_LOCKING and makes configuration of the different users of the tracepoints more easy and understandable. It also gets rid of the time_* function calls from the lockdep hooks used to call into the preemptirq tracer which is not needed anymore. The negative delta in lines of code in this patch is quite large too.
In the patch we introduce a new CONFIG option PREEMPTIRQ_TRACEPOINTS as a single point for registering probes onto the tracepoints. With this, the web of config options for preempt/irq toggle tracepoints and its users becomes:
PREEMPT_TRACER PREEMPTIRQ_EVENTS IRQSOFF_TRACER PROVE_LOCKING | | \ | | \ (selects) / \ \ (selects) / TRACE_PREEMPT_TOGGLE ----> TRACE_IRQFLAGS \ / \ (depends on) / PREEMPTIRQ_TRACEPOINTS
One note, I have to check for lockdep recursion in the code that calls the trace events API and bail out if we're in lockdep recursion protection to prevent something like the following case: a spin_lock is taken. Then lockdep_acquired is called. That does a raw_local_irq_save and then sets lockdep_recursion, and then calls __lockdep_acquired. In this function, a call to get_lock_stats happens which calls preempt_disable, which calls trace IRQS off somewhere which enters my tracepoint code and sets the tracing_irq_cpu flag to prevent recursion. This flag is then never cleared causing lockdep paths to never be entered and thus causing splats and other bad things.
Other than the performance tests mentioned in the previous patch, I also ran the locking API test suite. I verified that all tests cases are passing.
I also injected issues by not registering lockdep probes onto the tracepoints and I see failures to confirm that the probes are indeed working.
Without probes:
[ 0.000000] hard-irqs-on + irq-safe-A/21: ok | ok | ok | [ 0.000000] soft-irqs-on + irq-safe-A/21: ok | ok | ok | [ 0.000000] sirq-safe-A => hirqs-on/12: ok | ok | ok | [ 0.000000] sirq-safe-A => hirqs-on/21: ok | ok | ok | [ 0.000000] hard-safe-A + irqs-on/12: ok | ok | ok | [ 0.000000] soft-safe-A + irqs-on/12: ok | ok | ok | [ 0.000000] hard-safe-A + irqs-on/21: ok | ok | ok | [ 0.000000] soft-safe-A + irqs-on/21: ok | ok | ok | [ 0.000000] hard-safe-A + unsafe-B #1/123: ok | ok | ok | [ 0.000000] soft-safe-A + unsafe-B #1/123: ok | ok | ok |
With probes:
[ 0.000000] hard-irqs-on + irq-safe-A/21: ok | ok | ok | [ 0.000000] soft-irqs-on + irq-safe-A/21: ok | ok | ok | [ 0.000000] sirq-safe-A => hirqs-on/12:FAILED|FAILED| ok | [ 0.000000] sirq-safe-A => hirqs-on/21:FAILED|FAILED| ok | [ 0.000000] hard-safe-A + irqs-on/12:FAILED|FAILED| ok | [ 0.000000] soft-safe-A + irqs-on/12:FAILED|FAILED| ok | [ 0.000000] hard-safe-A + irqs-on/21:FAILED|FAILED| ok | [ 0.000000] soft-safe-A + irqs-on/21:FAILED|FAILED| ok | [ 0.000000] hard-safe-A + unsafe-B #1/123: ok | ok | ok | [ 0.000000] soft-safe-A + unsafe-B #1/123: ok | ok | ok |
Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org
[SNIP]
#ifdef CONFIG_IRQSOFF_TRACER +/*
- We are only interested in hardirq on/off events:
- */
+static void tracer_hardirqs_on(void *none, unsigned long a0, unsigned long a1) +{
- if (!preempt_trace() && irq_trace())
stop_critical_timing(a0, a1);+}
+static void tracer_hardirqs_off(void *none, unsigned long a0, unsigned long a1) +{
- if (!preempt_trace() && irq_trace())
start_critical_timing(a0, a1);+}
static int irqsoff_tracer_init(struct trace_array *tr) { trace_type = TRACER_IRQS_OFF;
- register_trace_irq_disable(tracer_hardirqs_off, NULL);
- register_trace_irq_enable(tracer_hardirqs_on, NULL); return __irqsoff_tracer_init(tr);
} static void irqsoff_tracer_reset(struct trace_array *tr) {
- unregister_trace_irq_disable(tracer_hardirqs_off, NULL);
- unregister_trace_irq_enable(tracer_hardirqs_on, NULL); __irqsoff_tracer_reset(tr);
} @@ -692,19 +650,37 @@ static struct tracer irqsoff_tracer __read_mostly = }; # define register_irqsoff(trace) register_tracer(&trace) #else +static inline void tracer_hardirqs_on(unsigned long a0, unsigned long a1) { } +static inline void tracer_hardirqs_off(unsigned long a0, unsigned long a1) { }
Just a nitpick. These lines seem unnecessary since they're used only when CONFIG_IRQSOFF_TRACER is enabled AFAICS.
# define register_irqsoff(trace) do { } while (0) -#endif +#endif /* CONFIG_IRQSOFF_TRACER */ #ifdef CONFIG_PREEMPT_TRACER +static void tracer_preempt_on(void *none, unsigned long a0, unsigned long a1) +{
- if (preempt_trace() && !irq_trace())
stop_critical_timing(a0, a1);+}
+static void tracer_preempt_off(void *none, unsigned long a0, unsigned long a1) +{
- if (preempt_trace() && !irq_trace())
start_critical_timing(a0, a1);+}
static int preemptoff_tracer_init(struct trace_array *tr) { trace_type = TRACER_PREEMPT_OFF;
- register_trace_preempt_disable(tracer_preempt_off, NULL);
- register_trace_preempt_enable(tracer_preempt_on, NULL); return __irqsoff_tracer_init(tr);
} static void preemptoff_tracer_reset(struct trace_array *tr) {
- unregister_trace_preempt_disable(tracer_preempt_off, NULL);
- unregister_trace_preempt_enable(tracer_preempt_on, NULL); __irqsoff_tracer_reset(tr);
} @@ -729,21 +705,32 @@ static struct tracer preemptoff_tracer __read_mostly = }; # define register_preemptoff(trace) register_tracer(&trace) #else +static inline void tracer_preempt_on(unsigned long a0, unsigned long a1) { } +static inline void tracer_preempt_off(unsigned long a0, unsigned long a1) { }
Ditto (for CONFIG_PREEMPT_TRACER).
Thanks, Namhyung
# define register_preemptoff(trace) do { } while (0) -#endif +#endif /* CONFIG_PREEMPT_TRACER */ -#if defined(CONFIG_IRQSOFF_TRACER) && \
- defined(CONFIG_PREEMPT_TRACER)
+#if defined(CONFIG_IRQSOFF_TRACER) && defined(CONFIG_PREEMPT_TRACER) static int preemptirqsoff_tracer_init(struct trace_array *tr) { trace_type = TRACER_IRQS_OFF | TRACER_PREEMPT_OFF;
- register_trace_irq_disable(tracer_hardirqs_off, NULL);
- register_trace_irq_enable(tracer_hardirqs_on, NULL);
- register_trace_preempt_disable(tracer_preempt_off, NULL);
- register_trace_preempt_enable(tracer_preempt_on, NULL);
- return __irqsoff_tracer_init(tr);
} static void preemptirqsoff_tracer_reset(struct trace_array *tr) {
- unregister_trace_irq_disable(tracer_hardirqs_off, NULL);
- unregister_trace_irq_enable(tracer_hardirqs_on, NULL);
- unregister_trace_preempt_disable(tracer_preempt_off, NULL);
- unregister_trace_preempt_enable(tracer_preempt_on, NULL);
- __irqsoff_tracer_reset(tr);
}
-- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html