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* Deadlock with FTrace in child process
@ 2019-10-19  7:50 Allende Imanol
  2019-10-21 14:41 ` Steven Rostedt
  0 siblings, 1 reply; 4+ messages in thread
From: Allende Imanol @ 2019-10-19  7:50 UTC (permalink / raw)
  To: linux-trace-devel; +Cc: rostedt, mingo

I am using Ftrace in a Ultra96 (arm64) 4.19.75-cip11 and it seems that
I have a deadlock situation. I have a simple application executed as a
child process from a python script. The child process reads from
/dev/urandom and writes in /dev/zero. Ftrace is set only for this child
process.

After thousands of executions of the child process with a high IRQ and
CPU load (it varies in the number but it is quite reproducible) - the child
process gets blocked. But the system still is running.

The child process appears as "sleeping state" and if I try to do kill
-18 $pid it does not change.

In this case the child process is 4197 PID.

# ps -aux | grep python
root      1145  6.3  0.4  85448  9508 ?        S<l  00:00  23:02 python3 test_client.py
root      4197  0.0  0.4  85448  8256 ?        S<   05:53   0:00 python3 test_client.py
root      5279  0.0  0.0   2752   280 ttyPS0   S+   06:02   0:00 grep python
# cat /proc/4197/stack
[<0>] __switch_to+0x94/0xd0
[<0>] futex_wait_queue_me+0xd0/0x150
[<0>] futex_wait+0x12c/0x200
[<0>] do_futex+0x304/0xc10
[<0>] __arm64_sys_futex+0x154/0x190
[<0>] el0_svc_common+0xa0/0x170
[<0>] el0_svc_handler+0x38/0x80
[<0>] el0_svc+0x8/0xc
[<0>] 0xffffffffffffffff


The stack is more or less the same every time the block happens.

If I kill -9 the child process the execution loop will continue with
spawning the next child so it seems that the deadlock is really only
in the child process - but do not know why.

I am using function_graph traces and I added the funcgraph-proc,
noirq-info and nofuncgraphs-irq options. I disable tracing after each 
iteration, and I clear the trace buffer and pid set also.

I add the application that is executed as the child process:

#define DEV1 "/dev/urandom"
#define DEV2 "/dev/null"

int main(int argc, char **argv)
{
 unsigned char result;
 int fd1, fd2, ret;
 char res_str[10] = {0};

 fd1 = open(DEV1, O_RDONLY);
 fd2 = open(DEV2, O_WRONLY);

 ret = read(fd1, &result, 1);
 sprintf(res_str, "%d", result);
 ret = write(fd2, res_str, strlen(res_str));

 close(fd1);
 close(fd2);

 return ret;
}

The preemption configuration is set to Preemptible kernel and the Ftrace
config is set:
CONFIG_FTRACE=y
CONFIG_FUNCTION_TRACER=y
CONFIG_FUNCTION_GRAPH_TRACER=y
# CONFIG_PREEMPTIRQ_EVENTS is not set
# CONFIG_IRQSOFF_TRACER is not set
# CONFIG_PREEMPT_TRACER is not set
# CONFIG_SCHED_TRACER is not set
# CONFIG_HWLAT_TRACER is not set
CONFIG_FTRACE_SYSCALLS=y
# CONFIG_TRACER_SNAPSHOT is not set
CONFIG_BRANCH_PROFILE_NONE=y
# CONFIG_PROFILE_ANNOTATED_BRANCHES is not set
# CONFIG_PROFILE_ALL_BRANCHES is not set
CONFIG_STACK_TRACER=y
# CONFIG_BLK_DEV_IO_TRACE is not set
CONFIG_UPROBE_EVENTS=y
CONFIG_PROBE_EVENTS=y
CONFIG_DYNAMIC_FTRACE=y
# CONFIG_FUNCTION_PROFILER is not set
CONFIG_FTRACE_MCOUNT_RECORD=y
# CONFIG_FTRACE_STARTUP_TEST is not set
# CONFIG_HIST_TRIGGERS is not set
# CONFIG_TRACEPOINT_BENCHMARK is not set
# CONFIG_RING_BUFFER_BENCHMARK is not set
# CONFIG_RING_BUFFER_STARTUP_TEST is not set
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set
# CONFIG_TRACE_EVAL_MAP_FILE is not set
CONFIG_TRACING_EVENTS_GPIO=y


^ permalink raw reply	[flat|nested] 4+ messages in thread

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2019-10-19  7:50 Deadlock with FTrace in child process Allende Imanol
2019-10-21 14:41 ` Steven Rostedt
2019-10-25  0:44   ` Allende Imanol
2019-10-25  1:18     ` Steven Rostedt

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