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Message-ID: <53530AF7.7020807@insigma.com.cn> Date: Sun, 20 Apr 2014 07:47:03 +0800 From: Jiaxing Wang <wangjiaxing@...igma.com.cn> To: Steven Rostedt <rostedt@...dmis.org> CC: Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] tracing:Do not profile dumpstack utilities to fix stack trace output On 04/19/2014 11:18 PM, Steven Rostedt wrote: > On Sat, 19 Apr 2014 15:45:46 +0800 > Jiaxing Wang <wangjiaxing@...igma.com.cn> wrote: > >> When function_graph tracer is enabled, we get stack trace like this: >> >> Depth Size Location (88 entries) >> ----- ---- -------- >> 0) 3232 0 update_curr+0xe/0x1e0 >> 1) 3232 0 dump_trace+0xb5/0x1b0 >> 2) 3232 0 ftrace_ops_list_func+0xe6/0x100 >> 3) 3232 68 ftrace_call+0x5/0xb >> 4) 3164 92 enqueue_entity+0x38/0xe20 >> 5) 3072 0 return_to_handler+0x0/0xf >> 6) 3072 80 save_stack_trace+0x30/0x50 >> 7) 2992 0 return_to_handler+0x0/0xf >> 8) 2992 28 stack_trace_call+0x119/0x340 >> 9) 2964 0 return_to_handler+0x0/0xf >> 10) 2964 12 enqueue_task_fair+0x47/0x7e0 >> 11) 2952 0 return_to_handler+0x0/0xf >> 12) 2952 16 enqueue_task+0x45/0x70 >> ... ... >> >> The 'save_stack_trace+0x30/0x50' and 'stack_trace_call+0x119/0x340' >> entries are misplaced below the ftrace_ops_list_func and ftrace_call entries, >> which looks very confusing. >> >> And dump_stack() is also affected when function_graph tracer is enabled: >> >> [ 425.353391] Call Trace: >> [ 425.353449] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.353496] [<c1012546>] print_context_stack+0xc6/0xd0 >> [ 425.353547] [<c108ab84>] enqueue_entity+0x894/0xe60 >> [ 425.353597] [<c107b4c5>] ? enqueue_task+0x45/0x70 >> [ 425.353649] [<c108b159>] ? enqueue_task_fair+0x9/0x7e0 >> [ 425.353694] [<c107b4c5>] ? enqueue_task+0x45/0x70 >> [ 425.353743] [<c1041037>] ? prepare_ftrace_return+0x77/0xa0 >> [ 425.353791] [<c108b159>] ? enqueue_task_fair+0x9/0x7e0 >> [ 425.353856] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.353901] [<c10116b5>] dump_trace+0xb5/0x1b0 >> [ 425.353958] [<c107b4dd>] ? enqueue_task+0x5d/0x70 >> [ 425.354002] [<c107b436>] ? update_rq_clock.part.80+0x6/0x50 >> [ 425.354074] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354120] [<c1012666>] show_trace_log_lvl+0x46/0x50 >> [ 425.354178] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354222] [<c1011802>] show_stack_log_lvl+0x52/0xe0 >> [ 425.354272] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354317] [<c10126c6>] show_stack+0x26/0x50 >> [ 425.354369] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354415] [<c1643be1>] dump_stack+0x41/0x52 >> [ 425.354483] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354527] [<c108b197>] enqueue_task_fair+0x47/0x7e0 >> [ 425.354576] [<c16531c1>] ftrace_graph_caller+0x19/0x19 >> [ 425.354621] [<c107b4c5>] enqueue_task+0x45/0x70 >> ... ... >> >> This happens because the functions in the route of stack_trace and >> dump_stack() get function_graph traced, their return addresses on stack are >> replaced by 'return_to_handler' and their real return addresses are >> saved in current->ret_stack[].(Specifically, these functons include >> save_stack_trace,dump_trace,print_context_stack,print_ftrace_graph_addr >> in the case of stack_trace and show_stack,show_stack_log_lvl,show_trace_log_lvl >> ,dump_trace,print_context_stack,print_ftrace_graph_addr in the case of >> dump_stack()). >> >> When dumping the stack, their 'return_to_handler' on stack are skipped >> but not their corresponding current->ret_stack entries which then are matched >> with other function's 'return_to_handler' on the stack and resulting the >> wrong output above. > > This sounds like a separate bug that should be fixed. > Return addresses are skipped as stack_trace dump stack from the return address of dump_trace() and dump_stack() dump stack from the return address of show_stack(). Here is the stack_trace case: stack current->ret_stack[] ----- -------------------- return_to_handler print_context_stack+0xc6/0xd0 return_to_handler dump_trace+0xb5/0x1b0 return_to_handler save_stack_trace+0x30/0x50 return_to_handler stack_trace_call+0x119/0x340 ftrace_ops_listfunc+0xe6/0x100 ftrace_call+0x5/0xb So when dump, the first two 'return_to_handler' entries are skipped but not the current->ret_stack[] entries. And the following is the dump_stack() case: stack current->ret_stack[] ----- -------------------- return_to_handler print_context_stack+0xc6/0xd0 return_to_handler dump_trace+0xb5/0x1b0 return_to_handler show_trace_log_lvl+0x46/0x50 return_to_handler show_stack_log_lvl+0x52/0xe0 return_to_handler show_stack+0x26/0x50 return_to_handler dump_stack+0x41/0x52 In this case the first five 'return_to_handler' entries on stack are skipped but not the current->ret_stack[] entries. So the problem is caused by dumpstack utilities get traced by function_graph tracer, and disable the profiling of them fixes this. Thanks. >> >> To fix this, we can disable the profiling of dumpstack utilities. >> >> Signed-off-by: Jiaxing Wang <wangjiaxing@...igma.com.cn> >> --- >> arch/x86/kernel/Makefile | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile >> index f4d9600..9dd8ce4 100644 >> --- a/arch/x86/kernel/Makefile >> +++ b/arch/x86/kernel/Makefile >> @@ -14,6 +14,9 @@ CFLAGS_REMOVE_pvclock.o = -pg >> CFLAGS_REMOVE_kvmclock.o = -pg >> CFLAGS_REMOVE_ftrace.o = -pg >> CFLAGS_REMOVE_early_printk.o = -pg >> +CFLAGS_REMOVE_dumpstack.o = -pg >> +CFLAGS_REMOVE_dumpstack_32.o = -pg >> +CFLAGS_REMOVE_stacktrace.o = -pg > > I have no problem with this change, but it is 3.16 material. But if the > function graph tracer is causing the stack trace to be incorrect, then > that is a separate issues that we should try to rectify. > > -- Steve > >> endif >> >> CFLAGS_irq.o := -I$(src)/../include/asm/trace > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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