forked from Minki/linux
tracing: Remove most or all of stack tracer stack size from stack_max_size
Currently, the depth reported in the stack tracer stack_trace file does not match the stack_max_size file. This is because the stack_max_size includes the overhead of stack tracer itself while the depth does not. The first time a max is triggered, a calculation is not performed that figures out the overhead of the stack tracer and subtracts it from the stack_max_size variable. The overhead is stored and is subtracted from the reported stack size for comparing for a new max. Now the stack_max_size corresponds to the reported depth: # cat stack_max_size 4640 # cat stack_trace Depth Size Location (48 entries) ----- ---- -------- 0) 4640 32 _raw_spin_lock+0x18/0x24 1) 4608 112 ____cache_alloc+0xb7/0x22d 2) 4496 80 kmem_cache_alloc+0x63/0x12f 3) 4416 16 mempool_alloc_slab+0x15/0x17 [...] While testing against and older gcc on x86 that uses mcount instead of fentry, I found that pasing in ip + MCOUNT_INSN_SIZE let the stack trace show one more function deep which was missing before. Cc: stable@vger.kernel.org Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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@ -20,27 +20,24 @@
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#define STACK_TRACE_ENTRIES 500
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/*
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* If fentry is used, then the function being traced will
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* jump to fentry directly before it sets up its stack frame.
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* We need to ignore that one and record the parent. Since
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* the stack frame for the traced function wasn't set up yet,
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* the stack_trace wont see the parent. That needs to be added
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* manually to stack_dump_trace[] as the first element.
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*/
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#ifdef CC_USING_FENTRY
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# define add_func 1
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# define fentry 1
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#else
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# define add_func 0
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# define fentry 0
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#endif
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static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
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{ [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
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static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
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/*
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* Reserve one entry for the passed in ip. This will allow
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* us to remove most or all of the stack size overhead
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* added by the stack tracer itself.
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*/
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static struct stack_trace max_stack_trace = {
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.max_entries = STACK_TRACE_ENTRIES - add_func,
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.entries = &stack_dump_trace[add_func],
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.max_entries = STACK_TRACE_ENTRIES - 1,
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.entries = &stack_dump_trace[1],
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};
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static unsigned long max_stack_size;
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@ -58,10 +55,14 @@ check_stack(unsigned long ip, unsigned long *stack)
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{
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unsigned long this_size, flags;
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unsigned long *p, *top, *start;
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static int tracer_frame;
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int frame_size = ACCESS_ONCE(tracer_frame);
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int i;
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this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
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this_size = THREAD_SIZE - this_size;
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/* Remove the frame of the tracer */
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this_size -= frame_size;
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if (this_size <= max_stack_size)
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return;
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@ -73,6 +74,10 @@ check_stack(unsigned long ip, unsigned long *stack)
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local_irq_save(flags);
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arch_spin_lock(&max_stack_lock);
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/* In case another CPU set the tracer_frame on us */
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if (unlikely(!frame_size))
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this_size -= tracer_frame;
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/* a race could have already updated it */
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if (this_size <= max_stack_size)
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goto out;
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@ -85,15 +90,12 @@ check_stack(unsigned long ip, unsigned long *stack)
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save_stack_trace(&max_stack_trace);
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/*
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* When fentry is used, the traced function does not get
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* its stack frame set up, and we lose the parent.
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* Add that one in manally. We set up save_stack_trace()
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* to not touch the first element in this case.
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* Add the passed in ip from the function tracer.
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* Searching for this on the stack will skip over
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* most of the overhead from the stack tracer itself.
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*/
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if (add_func) {
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stack_dump_trace[0] = ip;
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max_stack_trace.nr_entries++;
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}
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/*
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* Now find where in the stack these are.
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@ -123,6 +125,18 @@ check_stack(unsigned long ip, unsigned long *stack)
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found = 1;
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/* Start the search from here */
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start = p + 1;
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/*
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* We do not want to show the overhead
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* of the stack tracer stack in the
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* max stack. If we haven't figured
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* out what that is, then figure it out
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* now.
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*/
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if (unlikely(!tracer_frame) && i == 1) {
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tracer_frame = (p - stack) *
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sizeof(unsigned long);
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max_stack_size -= tracer_frame;
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}
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}
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}
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@ -149,7 +163,26 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
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if (per_cpu(trace_active, cpu)++ != 0)
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goto out;
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check_stack(parent_ip, &stack);
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/*
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* When fentry is used, the traced function does not get
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* its stack frame set up, and we lose the parent.
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* The ip is pretty useless because the function tracer
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* was called before that function set up its stack frame.
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* In this case, we use the parent ip.
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*
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* By adding the return address of either the parent ip
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* or the current ip we can disregard most of the stack usage
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* caused by the stack tracer itself.
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*
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* The function tracer always reports the address of where the
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* mcount call was, but the stack will hold the return address.
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*/
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if (fentry)
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ip = parent_ip;
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else
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ip += MCOUNT_INSN_SIZE;
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check_stack(ip, &stack);
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out:
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per_cpu(trace_active, cpu)--;
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