On Sat, Aug 31, 2013 at 01:11:31AM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org>
>
> When the RCU lockdep splat hits because of the unsafe RCU checker,
> the backtrace does not always show the culprit. But the culprit was
> passed to the unsafe RCU checker.
>
> Save the ip of the function being traced in a per_cpu variable, and
> when the RCU lockdep detects a problem, it can also print out what
> function was being traced if it was caused by the unsafe RCU checker.
>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Signed-off-by: Steven Rostedt <rost...@goodmis.org>
Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> include/linux/ftrace.h | 6 ++++++
> kernel/lockdep.c | 2 ++
> kernel/trace/trace_functions.c | 14 ++++++++++++++
> 3 files changed, 22 insertions(+)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 4752764..3dbb946 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -885,4 +885,10 @@ unsigned long arch_syscall_addr(int nr);
>
> #endif /* CONFIG_FTRACE_SYSCALLS */
>
> +#ifdef CONFIG_FTRACE_UNSAFE_RCU_CHECKER
> +extern void print_ftrace_rcu_func(int cpu);
> +#else
> +static inline void print_ftrace_rcu_func(int cpu) { }
> +#endif
> +
> #endif /* _LINUX_FTRACE_H */
> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> index e16c45b..74272ed 100644
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -4229,6 +4229,8 @@ void lockdep_rcu_suspicious(const char *file, const int
> line, const char *s)
> : "",
> rcu_scheduler_active, debug_locks);
>
> + print_ftrace_rcu_func(raw_smp_processor_id());
> +
> /*
> * If a CPU is in the RCU-free window in idle (ie: in the section
> * between rcu_idle_enter() and rcu_idle_exit(), then RCU
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> index 1d5f951..f5a9031 100644
> --- a/kernel/trace/trace_functions.c
> +++ b/kernel/trace/trace_functions.c
> @@ -560,6 +560,7 @@ static inline int init_func_cmd_traceon(void)
> #endif /* CONFIG_DYNAMIC_FTRACE */
>
> #ifdef CONFIG_FTRACE_UNSAFE_RCU_CHECKER
> +
> static atomic_t ftrace_unsafe_rcu_disabled;
>
> void ftrace_unsafe_rcu_checker_disable(void)
> @@ -572,6 +573,17 @@ void ftrace_unsafe_rcu_checker_enable(void)
> atomic_dec(&ftrace_unsafe_rcu_disabled);
> }
>
> +static DEFINE_PER_CPU(unsigned long, ftrace_rcu_func);
> +
> +void print_ftrace_rcu_func(int cpu)
> +{
> + unsigned long ip = per_cpu(ftrace_rcu_func, cpu);
> +
> + if (ip)
> + printk("ftrace_rcu_func: %pS\n",
> + (void *)per_cpu(ftrace_rcu_func, cpu));
> +}
> +
> static void
> ftrace_unsafe_callback(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *op, struct pt_regs *pt_regs)
> @@ -592,9 +604,11 @@ ftrace_unsafe_callback(unsigned long ip, unsigned long
> parent_ip,
> (void *)ip))
> goto out;
>
> + this_cpu_write(ftrace_rcu_func, ip);
> /* Should trigger a RCU splat if called from unsafe RCU function */
> rcu_read_lock();
> rcu_read_unlock();
> + this_cpu_write(ftrace_rcu_func, 0);
>
> trace_clear_recursion(bit);
> out:
> --
> 1.7.10.4
>
>
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