The initial implementation of stack tracing to function trace in
536149910130 ("ftrace: add stack trace to function tracer") required
5 call stack entries to be skipped to avoid polluting the resulting
stacks with ftrace functions. Commit 4104d326b670 ("ftrace: Remove
global function list and call function directly") removed some of
these. Additionally be54f69c2619 ("tracing: Skip more functions when
doing stack tracing of events") also added some logic to adjust the
filtering.The end result of all this shuffling of code is that the magic number 5 in function_stack_trace_call no longer corresponds to reality. This results in skipping more than we would like. For example without the this patch tracing vfs_open produces: trace-cmd stream -p function -l vfs_open --func-stack <...>-488 [003] 11.356514: function: vfs_open <...>-488 [003] 11.356516: kernel_stack: <stack trace> => do_sys_open (ffffffff811a64b7) => SyS_open (ffffffff811a65ae) => entry_SYSCALL_64_fastpath (ffffffff8180009b) Where as the correct stack trace should be : => vfs_open (ffffffff811a6085) => path_openat (ffffffff811b71af) => do_filp_open (ffffffff811b8a8a) => do_sys_open (ffffffff811a64a7) => SyS_open (ffffffff811a659e) => entry_SYSCALL_64_fastpath (ffffffff8180009b) Signed-off-by: Nikolay Borisov <[email protected]> --- Strange why __trace_stack and __ftrace_trace_stack are not part of the stack and don't need to be filtered, despite not being inlined: nm vmlinux | grep save_stack_trace_regs ffffffff81026fd0 T save_stack_trace_regs nm vmlinux | grep __save_stack_trace ffffffff81026e20 t __save_stack_trace kernel/trace/trace_functions.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c index 27f7ad12c4b1..b721f1f3f3c0 100644 --- a/kernel/trace/trace_functions.c +++ b/kernel/trace/trace_functions.c @@ -181,14 +181,11 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip, pc = preempt_count(); trace_function(tr, ip, parent_ip, flags, pc); /* - * skip over 5 funcs: - * __ftrace_trace_stack, - * __trace_stack, + * skip over 2 funcs: * function_stack_trace_call - * ftrace_list_func * ftrace_call */ - __trace_stack(tr, flags, 5, pc); + __trace_stack(tr, flags, 2, pc); } atomic_dec(&data->disabled); -- 2.7.4
