2012-10-30 01:26:46

by Liu, Chuansheng

Subject: [PATCH V2] hrtimer: Printing timer info when hitting BUG_ON()

We encounted one BUG_ON() issue at function __run_hrtimer(),
but the panic info is not enough to find out which hrtimer
users use the hrtimer wrongly.
(in this BUG_ON case, it is callback running at the same time
hrtimer_start() is executed on different context.)

We can print basic timer info before BUG(), it is easy to find
out which hrtimer user has fault, the output info is like below:

<3>[ 41.118552] timer info: state/3, func/test_timer_cb
<3>[ 41.118618] timer stats: pid/786(sh), site/hrtimer_start
<0>[ 41.118670] ------------[ cut here ]------------
<2>[ 41.118691] kernel BUG at /root/r4_code/hardware/intel/linux-2.6/kernel/hrtimer.c:1260!
<0>[ 41.118715] invalid opcode: 0000 [#1] PREEMPT SMP

The infos of callback/state are very helpful for debugging this BUG_ON().

Signed-off-by: Li Fei <[email protected]>
Signed-off-by: liu chuansheng <[email protected]>
---
kernel/hrtimer.c | 21 ++++++++++++++++++++-
1 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 6db7a5e..0618eaf 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1204,6 +1204,22 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
}
EXPORT_SYMBOL_GPL(hrtimer_get_res);

+/*
+ * dump_hrtimer_callinfo - print hrtimer information including:
+ * state, callback function, pid and start_site.
+*/
+static void dump_hrtimer_callinfo(struct hrtimer *timer)
+{
+
+ pr_err("timer info: state/%lx, func/%pf\n",
+ timer->state, timer->function);
+
+#ifdef CONFIG_TIMER_STATS
+ pr_err("timer stats: pid/%d(%s), site/%pf\n",
+ timer->start_pid, timer->start_comm, timer->start_site);
+#endif
+}
+
static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
{
struct hrtimer_clock_base *base = timer->base;
@@ -1235,7 +1251,10 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
* hrtimer_start_range_ns() or in hrtimer_interrupt()
*/
if (restart != HRTIMER_NORESTART) {
- BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
+ if (timer->state != HRTIMER_STATE_CALLBACK) {
+ dump_hrtimer_callinfo(timer);
+ BUG();
+ }
enqueue_hrtimer(timer, base);
}

--
1.7.0.4

2012-11-06 01:07:18

by Yanmin Zhang

Subject: Re: [PATCH V2] hrtimer: Printing timer info when hitting BUG_ON()

On Tue, 2012-10-30 at 18:27 +0800, Chuansheng Liu wrote:
> We encounted one BUG_ON() issue at function __run_hrtimer(),
> but the panic info is not enough to find out which hrtimer
> users use the hrtimer wrongly.
> (in this BUG_ON case, it is callback running at the same time
> hrtimer_start() is executed on different context.)
>
> We can print basic timer info before BUG(), it is easy to find
> out which hrtimer user has fault, the output info is like below:
>
> <3>[ 41.118552] timer info: state/3, func/test_timer_cb
> <3>[ 41.118618] timer stats: pid/786(sh), site/hrtimer_start
> <0>[ 41.118670] ------------[ cut here ]------------
> <2>[ 41.118691] kernel BUG at /root/r4_code/hardware/intel/linux-2.6/kernel/hrtimer.c:1260!
> <0>[ 41.118715] invalid opcode: 0000 [#1] PREEMPT SMP
>
> The infos of callback/state are very helpful for debugging this BUG_ON().
It's a useful patch.

Thomas,

Could you merge it into your testing tree, so other developers could also
benefit from it?

Thanks all.
Yanmin

>
> Signed-off-by: Li Fei <[email protected]>
> Signed-off-by: liu chuansheng <[email protected]>
> ---
> kernel/hrtimer.c | 21 ++++++++++++++++++++-
> 1 files changed, 20 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index 6db7a5e..0618eaf 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1204,6 +1204,22 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
> }
> EXPORT_SYMBOL_GPL(hrtimer_get_res);
>
> +/*
> + * dump_hrtimer_callinfo - print hrtimer information including:
> + * state, callback function, pid and start_site.
> +*/
> +static void dump_hrtimer_callinfo(struct hrtimer *timer)
> +{
> +
> + pr_err("timer info: state/%lx, func/%pf\n",
> + timer->state, timer->function);
> +
> +#ifdef CONFIG_TIMER_STATS
> + pr_err("timer stats: pid/%d(%s), site/%pf\n",
> + timer->start_pid, timer->start_comm, timer->start_site);
> +#endif
> +}
> +
> static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
> {
> struct hrtimer_clock_base *base = timer->base;
> @@ -1235,7 +1251,10 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
> * hrtimer_start_range_ns() or in hrtimer_interrupt()
> */
> if (restart != HRTIMER_NORESTART) {
> - BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
> + if (timer->state != HRTIMER_STATE_CALLBACK) {
> + dump_hrtimer_callinfo(timer);
> + BUG();
> + }
> enqueue_hrtimer(timer, base);
> }
>