On Wed, 23 Jul 2014 19:05:52 +0200 Oleg Nesterov <[email protected]> wrote:
> > kprobe ftrace_ops are allocated which sets the FTRACE_OPS_FL_DYNAMIC > > flag. You'll see that flag checked in update_ftrace_function(), and if > > it is set, it forces the ftrace_ops_list_func() to be used. > > No? __register_ftrace_function() sets if !core_kernel_data(ops), and > kprobe_ftrace_ops is not dynamic? Oh, you're right. I thought it was allocated. What it is missing is the FTRACE_OPS_RECURSION_SAFE flag. Although, I'm working on a patch that makes a non loop func that does the recursion checks for just a single ftrace_ops->func if only one is registered. > > > Why? > > > > [...snip..] > > Yes, thanks, I understand why, at least to some degree. > > > foo() > > [mcount called --> ftrace_caller trampoline] > > ftrace_caller > > load ftrace_ops into parameter > > <interrupt> > > preempt_schedule() > > [new task] > > kfree(kprobe ftrace_ops); > > see above. > > And to be sure, I compiled your rfc/trampoline kernel which I pulled > yesterday with the same patch and did the same test. __ftrace_ops_list_func() > prints nothing. Note, I'm still working on fixes to that branch ;-) > > So I also added WARN_ON(1) into kprobe_ftrace_handler() to ensure that > it is actually called, and yes, dmesg reports > > WARNING: ... kprobe_ftrace_handler+0x38/0x140() > ... > Call Trace: > [<ffffffff8136a3eb>] dump_stack+0x5b/0xa8 > [<ffffffff810423ec>] warn_slowpath_common+0x8c/0xc0 > [<ffffffff8105772c>] ? SyS_prctl+0x1c/0x730 > [<ffffffff8104243a>] warn_slowpath_null+0x1a/0x20 > [<ffffffff810325c8>] kprobe_ftrace_handler+0x38/0x140 > [<ffffffff8137148a>] ? retint_swapgs+0xe/0x13 > [<ffffffff81057731>] ? SyS_prctl+0x21/0x730 > [<ffffffff81057731>] ? SyS_prctl+0x21/0x730 > [<ffffffff8122424e>] ? trace_hardirqs_on_thunk+0x3a/0x3f > [<ffffffff81370912>] ? system_call_fastpath+0x16/0x1b > BTW, you may want to look at /sys/kernel/debug/tracing/enabled_functions as that has a lot of debug info for the trampolines in that branch. > after "perl -e 'syscall 157,-1'". > > and, as expected, if I do "echo SyS_prctl >| set_ftrace_filter" and > "echo function >| current_tracer", then the command above also triggers > 2 printk's in __ftrace_ops_list_func() : > > LIST_FUNC -> function_trace_call() > LIST_FUNC -> kprobe_ftrace_handler() > > so it seems that your patches can potentially buy more than you think ;) > > Oleg. I'll play with this some more to understand everything you are stating. Thanks, -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
