Messages in this thread Patch in this message | | | Date | Thu, 5 Jun 2008 16:54:05 -0400 (EDT) | From | Steven Rostedt <> | Subject | [PATCH] ftrace: disable function tracing bringing up new CPU |
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Peter Zijlstra found that taking down and bringing up a new CPU caused ftrace to crash the kernel. This was due to some arch calls that were being traced by the function tracer before the smp_processor_id was set up. Since the function tracer uses smp_processor_id it caused a triple fault.
Instead of adding notrace all over the architecture code to prevent this problem, it is easier to simply disable the function tracer when bringing up a new CPU.
Signed-off-by: Steven Rostedt <srostedt@redhat.com> --- include/linux/ftrace.h | 11 ++++++++--- kernel/cpu.c | 9 +++++++++ kernel/trace/ftrace.c | 28 ++++++++++++++++++++++++++++ kernel/trace/trace_irqsoff.c | 3 +++ kernel/trace/trace_sched_wakeup.c | 2 +- 5 files changed, 49 insertions(+), 4 deletions(-)
Index: linux-tip.git/include/linux/ftrace.h =================================================================== --- linux-tip.git.orig/include/linux/ftrace.h 2008-06-05 14:51:47.000000000 -0400 +++ linux-tip.git/include/linux/ftrace.h 2008-06-05 16:52:32.000000000 -0400 @@ -33,10 +33,15 @@ void clear_ftrace_function(void); extern void ftrace_stub(unsigned long a0, unsigned long a1); extern void mcount(void);
+void ftrace_enable(void); +void ftrace_disable(void); + #else /* !CONFIG_FTRACE */ -# define register_ftrace_function(ops) do { } while (0) -# define unregister_ftrace_function(ops) do { } while (0) -# define clear_ftrace_function(ops) do { } while (0) +# define register_ftrace_function(ops) do { } while (0) +# define unregister_ftrace_function(ops) do { } while (0) +# define clear_ftrace_function(ops) do { } while (0) +# define ftrace_enable() do { } while (0) +# define ftrace_disable() do { } while (0) #endif /* CONFIG_FTRACE */
#ifdef CONFIG_DYNAMIC_FTRACE Index: linux-tip.git/kernel/cpu.c =================================================================== --- linux-tip.git.orig/kernel/cpu.c 2008-06-05 14:50:44.000000000 -0400 +++ linux-tip.git/kernel/cpu.c 2008-06-05 14:51:50.000000000 -0400 @@ -14,6 +14,7 @@ #include <linux/kthread.h> #include <linux/stop_machine.h> #include <linux/mutex.h> +#include <linux/ftrace.h>
/* Serializes the updates to cpu_online_map, cpu_present_map */ static DEFINE_MUTEX(cpu_add_remove_lock); @@ -300,8 +301,16 @@ static int __cpuinit _cpu_up(unsigned in goto out_notify; }
+ /* + * Disable function tracing while bringing up a new CPU. + * We don't want to trace functions that can not handle a + * smp_processor_id() call. + */ + ftrace_disable(); + /* Arch-specific enabling code. */ ret = __cpu_up(cpu); + ftrace_enable(); if (ret != 0) goto out_notify; BUG_ON(!cpu_online(cpu)); Index: linux-tip.git/kernel/trace/ftrace.c =================================================================== --- linux-tip.git.orig/kernel/trace/ftrace.c 2008-06-05 14:50:44.000000000 -0400 +++ linux-tip.git/kernel/trace/ftrace.c 2008-06-05 16:41:09.000000000 -0400 @@ -148,6 +148,34 @@ static int __unregister_ftrace_function( return ret; }
+static int ftrace_disabled_count; +static int save_ftrace_enabled; + +void ftrace_disable(void) +{ + unsigned long flags; + + mutex_lock(&ftrace_sysctl_lock); + + save_ftrace_enabled = ftrace_enabled; + ftrace_enabled = 0; +} + +void ftrace_enable(void) +{ + unsigned long flags; + + /* ftrace_enable must be paired with ftrace_disable */ + if (!mutex_is_locked(&ftrace_sysctl_lock)) { + WARN_ON(1); + return; + } + + ftrace_enabled = save_ftrace_enabled; + + mutex_unlock(&ftrace_sysctl_lock); +} + #ifdef CONFIG_DYNAMIC_FTRACE
static struct task_struct *ftraced_task; Index: linux-tip.git/kernel/trace/trace_irqsoff.c =================================================================== --- linux-tip.git.orig/kernel/trace/trace_irqsoff.c 2008-06-05 14:50:44.000000000 -0400 +++ linux-tip.git/kernel/trace/trace_irqsoff.c 2008-06-05 14:51:50.000000000 -0400 @@ -76,6 +76,9 @@ irqsoff_tracer_call(unsigned long ip, un long disabled; int cpu;
+ if (unlikely(!ftrace_enabled)) + return; + /* * Does not matter if we preempt. We test the flags * afterward, to see if irqs are disabled or not. Index: linux-tip.git/kernel/trace/trace_sched_wakeup.c =================================================================== --- linux-tip.git.orig/kernel/trace/trace_sched_wakeup.c 2008-06-05 14:50:44.000000000 -0400 +++ linux-tip.git/kernel/trace/trace_sched_wakeup.c 2008-06-05 14:51:50.000000000 -0400 @@ -44,7 +44,7 @@ wakeup_tracer_call(unsigned long ip, uns int resched; int cpu;
- if (likely(!wakeup_task)) + if (likely(!wakeup_task) || !ftrace_enabled) return;
resched = need_resched();
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