On Sat, 19 Oct 2019 07:50:53 +0000
Allende Imanol <iallende@xxxxxxxxxx> wrote:
> 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.
Are you saying that ftrace is calling the blocked task?
If you don't run ftrace, the task never gets stuck?
>
> 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
Looks like the task is blocked on a user space mutex (futex).
> [<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:
I don't understand what you meant by this. Is the below the code that
gets stuck? But the above shows a python task?
>
> #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;
> }
Can you give the full reproducer, and explain the problem in a bit more
detail. I don't really see how ftrace is involved here, besides that
you are running it.
-- Steve
>
> 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
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