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Date: Wed, 17 Dec 2008 15:59:40 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Frederic Weisbecker <fweisbec@...il.com> Cc: mingo@...e.hu, rostedt@...dmis.org, tglx@...utronix.de, linux-kernel@...r.kernel.org Subject: Re: [PATCH] tracing/function-graph-tracer: prevent from hrtimer interrupt eternal loop On Thu, 18 Dec 2008 00:52:47 +0100 Frederic Weisbecker <fweisbec@...il.com> wrote: > Impact: fix a system hang on slow systems > > While testing the function graph tracer on VirtualBox, I had a system hang > immediately after enabling the tracer. > If hrtimer is enabled on kernel, a slow system can spend too much time during > tracing the hrtimer_interrupt which will do eternal loops, assuming it always > have to retry its process because too much time elapsed during its time > update. > Now we provide a feature which lurks at the number of retries on > hrtimer_interrupt. After 10 retries, the function graph tracer will finally stop > its tracing. > > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Steven Rostedt <rostedt@...dmis.org> > --- > arch/x86/kernel/ftrace.c | 2 ++ > include/linux/ftrace.h | 31 +++++++++++++++++++++++++++++++ > kernel/hrtimer.c | 5 +++++ > 3 files changed, 38 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 1b43086..244f178 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -389,6 +389,8 @@ void ftrace_nmi_exit(void) > > #endif /* !CONFIG_DYNAMIC_FTRACE */ > > +DEFINE_PER_CPU(int, ftrace_graph_hrtimer_loop) = LOCAL_INIT(0); Strange. This has type `int', but we initialise it with a local_t? > /* Add a function return address to the trace stack on thread info.*/ > static int push_return_trace(unsigned long ret, unsigned long long time, > unsigned long func, int *depth) > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 286af82..39be782 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -408,6 +408,34 @@ extern void unregister_ftrace_graph(void); > extern void ftrace_graph_init_task(struct task_struct *t); > extern void ftrace_graph_exit_task(struct task_struct *t); > > +/* > + * Those two functions prevent from eternal loops on hrtimer_interrupt "These two functions prevent infinite ..." > + * because the function graph tracer can cause two much time processing "can consume too much" > + * on slow systems, and the hrtimer_interrupt can relaunch its processing > + * if too much time elapsed during its previous time update. > + * > + * Note that we don't need an atomic counter for loops here because > + * interrupts are disabled in hrtimer_interrupt. > + */ > + > +extern DEFINE_PER_CPU(int, ftrace_graph_hrtimer_loop); We have DECLARE_PER_CPU() for this. > +static inline void ftrace_graph_hrtimer_enter(void) > +{ > + __get_cpu_var(ftrace_graph_hrtimer_loop) = 0; > +} > + > +static inline void ftrace_graph_hrtimer_retry(void) > +{ > + __get_cpu_var(ftrace_graph_hrtimer_loop)++; > + > + if (__get_cpu_var(ftrace_graph_hrtimer_loop) == 10) { > + ftrace_graph_stop(); > + printk(KERN_WARNING "function-graph-tracer: hrtimer_interrupt " > + "exceeded 10 loops. Stopping tracing\n"); > + } > +} I suspect this code would end up considerably neater (and less likely to break the build) if these functons were not inlined. For a start, ftrace_graph_hrtimer_loop would not need global scope. > static inline int task_curr_ret_stack(struct task_struct *t) > { > return t->curr_ret_stack; > @@ -437,6 +465,9 @@ static inline int task_curr_ret_stack(struct task_struct *tsk) > > static inline void pause_graph_tracing(void) { } > static inline void unpause_graph_tracing(void) { } > + > +static inline void ftrace_graph_hrtimer_enter(void) { }; > +static inline void ftrace_graph_hrtimer_retry(void) { }; Unneeded semicolons. Please consider doing static inline void ftrace_graph_hrtimer_enter(void) { } > #endif > > #ifdef CONFIG_TRACING > diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c > index b741f85..662eb53 100644 > --- a/kernel/hrtimer.c > +++ b/kernel/hrtimer.c > @@ -44,6 +44,7 @@ > #include <linux/seq_file.h> > #include <linux/err.h> > #include <linux/debugobjects.h> > +#include <linux/ftrace.h> > > #include <asm/uaccess.h> > > @@ -1186,7 +1187,11 @@ void hrtimer_interrupt(struct clock_event_device *dev) > cpu_base->nr_events++; > dev->next_event.tv64 = KTIME_MAX; > > + ftrace_graph_hrtimer_enter(); > retry: > + /* Prevent from eternal loop on slow systems while tracing */ > + ftrace_graph_hrtimer_retry(); > + > now = ktime_get(); > > expires_next.tv64 = KTIME_MAX; > -- > 1.6.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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