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Date: Thu, 26 May 2011 09:54:24 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Witold Baryluk <baryluk@....if.uj.edu.pl>
Subject: Re: [PATCH 12/12] ftrace: Add internal recursive checks
On Thu, May 26, 2011 at 11:25:54AM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
>
> Witold reported a reboot caused by the selftests of the dynamic function
> tracer. He sent me a config and I used ktest to do a config_bisect on it
> (as my config did not cause the crash). It pointed out that the problem
> config was CONFIG_PROVE_RCU.
>
> What happened was that if multiple callbacks are attached to the
> function tracer, we iterate a list of callbacks. Because the list is
> managed by synchronize_sched() and preempt_disable, the access to the
> pointers uses rcu_dereference_raw().
>
> When PROVE_RCU is enabled, the rcu_dereference_raw() calls some
> debugging functions, which happen to be traced. The tracing of the debug
> function would then call rcu_dereference_raw() which would then call the
> debug function and then... well you get the idea.
>
> I first wrote two different patches to solve this bug.
>
> 1) add a __rcu_dereference_raw() that would not do any checks.
> 2) add notrace to the offending debug functions.
>
> Both of these patches worked.
>
> Talking with Paul McKenney on IRC, he suggested to add recursion
> detection instead. This seemed to be a better solution, so I decided to
> implement it. As the task_struct already has a trace_recursion to detect
> recursion in the ring buffer, and that has a very small number it
> allows, I decided to use that same variable to add flags that can detect
> the recursion inside the infrastructure of the function tracer.
>
> I plan to change it so that the task struct bit can be checked in
> mcount, but as that requires changes to all archs, I will hold that off
> to the next merge window.
Looks good to me.
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Link: http://lkml.kernel.org/r/1306348063.1465.116.camel@gandalf.stny.rr.com
> Reported-by: Witold Baryluk <baryluk@....if.uj.edu.pl>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> include/linux/sched.h | 2 +-
> kernel/trace/ftrace.c | 13 ++++++++++++-
> kernel/trace/ring_buffer.c | 10 +++++-----
> kernel/trace/trace.h | 15 +++++++++++++++
> 4 files changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d8b2d0b..7b78d9c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1513,7 +1513,7 @@ struct task_struct {
> #ifdef CONFIG_TRACING
> /* state flags for use by tracers */
> unsigned long trace;
> - /* bitmask of trace recursion */
> + /* bitmask and counter of trace recursion */
> unsigned long trace_recursion;
> #endif /* CONFIG_TRACING */
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR /* memcg uses this to do batch job */
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 25949b3..1ee417f 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -109,12 +109,18 @@ ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip);
> static void ftrace_global_list_func(unsigned long ip,
> unsigned long parent_ip)
> {
> - struct ftrace_ops *op = rcu_dereference_raw(ftrace_global_list); /*see above*/
> + struct ftrace_ops *op;
> +
> + if (unlikely(trace_recursion_test(TRACE_GLOBAL_BIT)))
> + return;
>
> + trace_recursion_set(TRACE_GLOBAL_BIT);
> + op = rcu_dereference_raw(ftrace_global_list); /*see above*/
> while (op != &ftrace_list_end) {
> op->func(ip, parent_ip);
> op = rcu_dereference_raw(op->next); /*see above*/
> };
> + trace_recursion_clear(TRACE_GLOBAL_BIT);
> }
>
> static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip)
> @@ -3490,6 +3496,10 @@ ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
> {
> struct ftrace_ops *op;
>
> + if (unlikely(trace_recursion_test(TRACE_INTERNAL_BIT)))
> + return;
> +
> + trace_recursion_set(TRACE_INTERNAL_BIT);
> /*
> * Some of the ops may be dynamically allocated,
> * they must be freed after a synchronize_sched().
> @@ -3502,6 +3512,7 @@ ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
> op = rcu_dereference_raw(op->next);
> };
> preempt_enable_notrace();
> + trace_recursion_clear(TRACE_INTERNAL_BIT);
> }
>
> static void clear_ftrace_swapper(void)
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 0ef7b4b..b0c7aa4 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -2216,7 +2216,7 @@ static noinline void trace_recursive_fail(void)
>
> printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
> "HC[%lu]:SC[%lu]:NMI[%lu]\n",
> - current->trace_recursion,
> + trace_recursion_buffer(),
> hardirq_count() >> HARDIRQ_SHIFT,
> softirq_count() >> SOFTIRQ_SHIFT,
> in_nmi());
> @@ -2226,9 +2226,9 @@ static noinline void trace_recursive_fail(void)
>
> static inline int trace_recursive_lock(void)
> {
> - current->trace_recursion++;
> + trace_recursion_inc();
>
> - if (likely(current->trace_recursion < TRACE_RECURSIVE_DEPTH))
> + if (likely(trace_recursion_buffer() < TRACE_RECURSIVE_DEPTH))
> return 0;
>
> trace_recursive_fail();
> @@ -2238,9 +2238,9 @@ static inline int trace_recursive_lock(void)
>
> static inline void trace_recursive_unlock(void)
> {
> - WARN_ON_ONCE(!current->trace_recursion);
> + WARN_ON_ONCE(!trace_recursion_buffer());
>
> - current->trace_recursion--;
> + trace_recursion_dec();
> }
>
> #else
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 6b69c4b..229f859 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -784,4 +784,19 @@ extern const char *__stop___trace_bprintk_fmt[];
> FTRACE_ENTRY(call, struct_name, id, PARAMS(tstruct), PARAMS(print))
> #include "trace_entries.h"
>
> +/* Only current can touch trace_recursion */
> +#define trace_recursion_inc() do { (current)->trace_recursion++; } while (0)
> +#define trace_recursion_dec() do { (current)->trace_recursion--; } while (0)
> +
> +/* Ring buffer has the 10 LSB bits to count */
> +#define trace_recursion_buffer() ((current)->trace_recursion & 0x3ff)
> +
> +/* for function tracing recursion */
> +#define TRACE_INTERNAL_BIT (1<<11)
> +#define TRACE_GLOBAL_BIT (1<<12)
> +
> +#define trace_recursion_set(bit) do { (current)->trace_recursion |= (bit); } while (0)
> +#define trace_recursion_clear(bit) do { (current)->trace_recursion &= ~(bit); } while (0)
> +#define trace_recursion_test(bit) ((current)->trace_recursion & (bit))
> +
> #endif /* _LINUX_KERNEL_TRACE_H */
> --
> 1.7.4.4
>
>
--
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