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authorSteven Rostedt <srostedt@redhat.com>2010-06-03 09:36:50 -0400
committerSteven Rostedt <rostedt@goodmis.org>2010-06-03 19:32:38 -0400
commit5168ae50a66e3ff7184c2b16d661bd6d70367e50 (patch)
tree2fb21fc3bd346e4f589605d940dfb1bacac30bf5 /kernel/trace/trace_sched_wakeup.c
parentd1f74e20b5b064a130cd0743a256c2d3cfe84010 (diff)
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tracing: Remove ftrace_preempt_disable/enable
The ftrace_preempt_disable/enable functions were to address a recursive race caused by the function tracer. The function tracer traces all functions which makes it easily susceptible to recursion. One area was preempt_enable(). This would call the scheduler and the schedulre would call the function tracer and loop. (So was it thought). The ftrace_preempt_disable/enable was made to protect against recursion inside the scheduler by storing the NEED_RESCHED flag. If it was set before the ftrace_preempt_disable() it would not call schedule on ftrace_preempt_enable(), thinking that if it was set before then it would have already scheduled unless it was already in the scheduler. This worked fine except in the case of SMP, where another task would set the NEED_RESCHED flag for a task on another CPU, and then kick off an IPI to trigger it. This could cause the NEED_RESCHED to be saved at ftrace_preempt_disable() but the IPI to arrive in the the preempt disabled section. The ftrace_preempt_enable() would not call the scheduler because the flag was already set before entring the section. This bug would cause a missed preemption check and cause lower latencies. Investigating further, I found that the recusion caused by the function tracer was not due to schedule(), but due to preempt_schedule(). Now that preempt_schedule is completely annotated with notrace, the recusion no longer is an issue. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace_sched_wakeup.c')
-rw-r--r--kernel/trace/trace_sched_wakeup.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 0e73bc2ef8c..c9fd5bd0203 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -46,7 +46,6 @@ wakeup_tracer_call(unsigned long ip, unsigned long parent_ip)
struct trace_array_cpu *data;
unsigned long flags;
long disabled;
- int resched;
int cpu;
int pc;
@@ -54,7 +53,7 @@ wakeup_tracer_call(unsigned long ip, unsigned long parent_ip)
return;
pc = preempt_count();
- resched = ftrace_preempt_disable();
+ preempt_disable_notrace();
cpu = raw_smp_processor_id();
if (cpu != wakeup_current_cpu)
@@ -74,7 +73,7 @@ wakeup_tracer_call(unsigned long ip, unsigned long parent_ip)
out:
atomic_dec(&data->disabled);
out_enable:
- ftrace_preempt_enable(resched);
+ preempt_enable_notrace();
}
static struct ftrace_ops trace_ops __read_mostly =