Hi Kefeng,
Thanks for catching this issue.
Please find my comments line -
On 6/8/20 12:54 AM, Kefeng Wang wrote:
> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:935
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/5
> 1 lock held by swapper/5/0:
> #0: ffff80001002bd90 (samples/ftrace/sample-trace-array.c:38){+.-.}-{0:0},
> at: call_timer_fn+0x8/0x3e0
> CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.7.0+ #8
> Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
> Call trace:
> dump_backtrace+0x0/0x1a0
> show_stack+0x20/0x30
> dump_stack+0xe4/0x150
> ___might_sleep+0x160/0x200
> __might_sleep+0x58/0x90
> __mutex_lock+0x64/0x948
> mutex_lock_nested+0x3c/0x58
> __ftrace_set_clr_event+0x44/0x88
> trace_array_set_clr_event+0x24/0x38
> mytimer_handler+0x34/0x40 [sample_trace_array]
>
> mutex_lock() will be called in interrupt context, using workqueueu to fix it.
/s/workqueueu/workqueue
Fixes: 89ed42495ef4 ("tracing: Sample module to demonstrate kernel access to
Ftrace instances.")
> Signed-off-by: Kefeng Wang <wangkefeng.w...@huawei.com>
> ---
> samples/ftrace/sample-trace-array.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/samples/ftrace/sample-trace-array.c
> b/samples/ftrace/sample-trace-array.c
> index d523450d73eb..41684c7dbd7b 100644
> --- a/samples/ftrace/sample-trace-array.c
> +++ b/samples/ftrace/sample-trace-array.c
> @@ -20,6 +20,16 @@ struct trace_array *tr;
> static void mytimer_handler(struct timer_list *unused);
> static struct task_struct *simple_tsk;
>
> +static void trace_work_fn(struct work_struct *work)
> +{
> + /*
> + * Disable tracing for event "sample_event".
> + */
> + trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
> + false);
> +}
> +static DECLARE_WORK(trace_work, trace_work_fn);
> +
> /*
> * mytimer: Timer setup to disable tracing for event "sample_event". This
> * timer is only for the purposes of the sample module to demonstrate access
> of
> @@ -29,11 +39,7 @@ static DEFINE_TIMER(mytimer, mytimer_handler);
>
> static void mytimer_handler(struct timer_list *unused)
> {
> - /*
> - * Disable tracing for event "sample_event".
> - */
> - trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
> - false);
> + schedule_work(&trace_work);
> }
>
> static void simple_thread_func(int count)
I think we also need to use cancel_work_sync() to handle the case -
1. Module unloaded
2. Timer already ran and scheduled work to disable trace event
3. When the work runs we no longer have the relevant trace array.
static int simple_thread(void *arg)
{
.....
del_timer(&mytimer);
<cancel_work_sync>
.....
return 0;
}
Thanks,
Divya
