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tracing: irqsoff: Account for additional preempt_disable 

Recently we tried to make the preemptirqsoff tracer to use irqsoff
tracepoint probes. However this causes issues as reported by Masami:

[2.271078] Testing tracer preemptirqsoff: .. no entries found ..FAILED!
[2.381015] WARNING: CPU: 0 PID: 1 at /home/mhiramat/ksrc/linux/kernel/
trace/trace.c:1512 run_tracer_selftest+0xf3/0x154

This is due to the tracepoint code increasing the preempt nesting count
by calling an additional preempt_disable before calling into the
preemptoff tracer which messes up the preempt_count() check in
tracer_hardirqs_off.

To fix this, make the irqsoff tracer probes balance the additional outer
preempt_disable with a preempt_enable_notrace.

The other way to fix this is to just use SRCU for all tracepoints.
However we can't do that because we can't use NMIs from RCU context.

Link: http://lkml.kernel.org/r/20180806034049.67949-1-joel@joelfernandes.org

Fixes: c3bc8fd637 ("tracing: Centralize preemptirq tracepoints and unify their usage")
Fixes: e6753f23d9 ("tracepoint: Make rcuidle tracepoint callers use SRCU")
Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Joel Fernandes (Google) 2018-08-05 20:40:49 -07:00 committed by Steven Rostedt (VMware)
parent da25a672cf
commit da5b3ebb45
1 changed files with 26 additions and 0 deletions
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26
kernel/trace/trace_irqsoff.c
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@ -603,14 +603,40 @@ static void irqsoff_tracer_stop(struct trace_array *tr)
*/ */
static void tracer_hardirqs_on(void *none, unsigned long a0, unsigned long a1) static void tracer_hardirqs_on(void *none, unsigned long a0, unsigned long a1)
{ {
/*
* Tracepoint probes are expected to be called with preempt disabled,
* We don't care about being called with preempt disabled but we need
* to know in the future if that changes so we can remove the next
* preempt_enable.
*/
WARN_ON_ONCE(!preempt_count());
/* Tracepoint probes disable preemption atleast once, account for that */
preempt_enable_notrace();
if (!preempt_trace() && irq_trace()) if (!preempt_trace() && irq_trace())
stop_critical_timing(a0, a1); stop_critical_timing(a0, a1);
preempt_disable_notrace();
} }
static void tracer_hardirqs_off(void *none, unsigned long a0, unsigned long a1) static void tracer_hardirqs_off(void *none, unsigned long a0, unsigned long a1)
{ {
/*
* Tracepoint probes are expected to be called with preempt disabled,
* We don't care about being called with preempt disabled but we need
* to know in the future if that changes so we can remove the next
* preempt_enable.
*/
WARN_ON_ONCE(!preempt_count());
/* Tracepoint probes disable preemption atleast once, account for that */
preempt_enable_notrace();
if (!preempt_trace() && irq_trace()) if (!preempt_trace() && irq_trace())
start_critical_timing(a0, a1); start_critical_timing(a0, a1);
preempt_disable_notrace();
} }
static int irqsoff_tracer_init(struct trace_array *tr) static int irqsoff_tracer_init(struct trace_array *tr)