On Sun, 4 Nov 2018 22:59:13 +1100 Aleksa Sarai cyphar@cyphar.com wrote:
The same issue is present in __save_stack_trace (arch/x86/kernel/stacktrace.c). This is likely the only reason that -- as Steven said -- stacktraces wouldn't work with ftrace-graph (and thus with the refactor both of you are discussing).
By the way, I was playing with the the orc unwinder and stack traces from the function graph tracer return code, and got it working with the below patch. Caution, that patch also has a stack trace hardcoded in the return path of the function graph tracer, so you don't want to run function graph tracing without filtering.
You can apply the patch and do:
# cd /sys/kernel/debug/tracing # echo schedule > set_ftrace_filter # echo function_graph > current_tracer # cat trace
3) | schedule() { rcu_preempt-10 [003] .... 91.160297: <stack trace> => ftrace_return_to_handler => return_to_handler => schedule_timeout => rcu_gp_kthread => kthread => ret_from_fork 3) # 4009.085 us | } 3) | schedule() { kworker/1:0-17 [001] .... 91.163288: <stack trace> => ftrace_return_to_handler => return_to_handler => worker_thread => kthread => ret_from_fork 1) # 7000.070 us | } 1) | schedule() { rcu_preempt-10 [003] .... 91.164311: <stack trace> => ftrace_return_to_handler => return_to_handler => schedule_timeout => rcu_gp_kthread => kthread => ret_from_fork 3) # 4006.540 us | }
Where just adding the stack trace without the other code, these traces ended at "return_to_handler".
This patch is not for inclusion, it was just a test to see how to make this work.
-- Steve
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index 91b2cff4b79a..4bcd646ae1f4 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -320,13 +320,15 @@ ENTRY(ftrace_graph_caller) ENDPROC(ftrace_graph_caller)
ENTRY(return_to_handler) - UNWIND_HINT_EMPTY - subq $24, %rsp + subq $8, %rsp + UNWIND_HINT_FUNC + subq $16, %rsp
/* Save the return values */ movq %rax, (%rsp) movq %rdx, 8(%rsp) movq %rbp, %rdi + leaq 16(%rsp), %rsi
call ftrace_return_to_handler
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c index 169b3c44ee97..aaeca73218cc 100644 --- a/kernel/trace/trace_functions_graph.c +++ b/kernel/trace/trace_functions_graph.c @@ -242,13 +242,16 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret, trace->calltime = current->ret_stack[index].calltime; trace->overrun = atomic_read(¤t->trace_overrun); trace->depth = index; + + trace_dump_stack(0); }
/* * Send the trace to the ring-buffer. * @return the original return address. */ -unsigned long ftrace_return_to_handler(unsigned long frame_pointer) +unsigned long ftrace_return_to_handler(unsigned long frame_pointer, + unsigned long *ptr) { struct ftrace_graph_ret trace; unsigned long ret; @@ -257,6 +260,8 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer) trace.rettime = trace_clock_local(); barrier(); current->curr_ret_stack--; + *ptr = ret; + /* * The curr_ret_stack can be less than -1 only if it was * filtered out and it's about to return from the function.