Messages in this thread | | | Date | Fri, 7 Apr 2017 07:36:19 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 2/5 v2] tracing: Replace the per_cpu() with this_cpu() in trace_stack.c |
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On Fri, Apr 07, 2017 at 10:01:08AM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > The updates to the trace_active per cpu variable can be updated with the > this_cpu_*() functions as it only gets updated on the CPU that the variable > is on. > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> > --- > kernel/trace/trace_stack.c | 23 +++++++---------------- > 1 file changed, 7 insertions(+), 16 deletions(-) > > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c > index 5fb1f2c87e6b..05ad2b86461e 100644 > --- a/kernel/trace/trace_stack.c > +++ b/kernel/trace/trace_stack.c > @@ -207,13 +207,12 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip, > struct ftrace_ops *op, struct pt_regs *pt_regs) > { > unsigned long stack; > - int cpu; > > preempt_disable_notrace(); > > - cpu = raw_smp_processor_id(); > /* no atomic needed, we only modify this variable by this cpu */ > - if (per_cpu(trace_active, cpu)++ != 0) > + this_cpu_inc(trace_active);
For whatever it is worth...
I was about to complain that this_cpu_inc() only disables preemption, not interrupts, but then I realized that any correct interrupt handler would have to restore the per-CPU variable to its original value.
Presumably you have to sum up all the per-CPU trace_active counts, given that there is no guarantee that a process-level dec will happen on the same CPU that did the inc.
Thanx, Paul
> + if (this_cpu_read(trace_active) != 1) > goto out; > > ip += MCOUNT_INSN_SIZE; > @@ -221,7 +220,7 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip, > check_stack(ip, &stack); > > out: > - per_cpu(trace_active, cpu)--; > + this_cpu_dec(trace_active); > /* prevent recursion in schedule */ > preempt_enable_notrace(); > } > @@ -253,7 +252,6 @@ stack_max_size_write(struct file *filp, const char __user *ubuf, > long *ptr = filp->private_data; > unsigned long val, flags; > int ret; > - int cpu; > > ret = kstrtoul_from_user(ubuf, count, 10, &val); > if (ret) > @@ -266,14 +264,13 @@ stack_max_size_write(struct file *filp, const char __user *ubuf, > * we will cause circular lock, so we also need to increase > * the percpu trace_active here. > */ > - cpu = smp_processor_id(); > - per_cpu(trace_active, cpu)++; > + this_cpu_inc(trace_active); > > arch_spin_lock(&stack_trace_max_lock); > *ptr = val; > arch_spin_unlock(&stack_trace_max_lock); > > - per_cpu(trace_active, cpu)--; > + this_cpu_dec(trace_active); > local_irq_restore(flags); > > return count; > @@ -307,12 +304,9 @@ t_next(struct seq_file *m, void *v, loff_t *pos) > > static void *t_start(struct seq_file *m, loff_t *pos) > { > - int cpu; > - > local_irq_disable(); > > - cpu = smp_processor_id(); > - per_cpu(trace_active, cpu)++; > + this_cpu_inc(trace_active); > > arch_spin_lock(&stack_trace_max_lock); > > @@ -324,12 +318,9 @@ static void *t_start(struct seq_file *m, loff_t *pos) > > static void t_stop(struct seq_file *m, void *p) > { > - int cpu; > - > arch_spin_unlock(&stack_trace_max_lock); > > - cpu = smp_processor_id(); > - per_cpu(trace_active, cpu)--; > + this_cpu_dec(trace_active); > > local_irq_enable(); > } > -- > 2.10.2 > >
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