Commit 4df29712 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

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: default avatarSteven Rostedt <rostedt@goodmis.org>
parent d4ecbfc4

kernel/trace/trace_stack.c

+54 −21
Original line number Diff line number Diff line
@@ -20,27 +20,24 @@ 


#define STACK_TRACE_ENTRIES 500



/*

 * If fentry is used, then the function being traced will

 * jump to fentry directly before it sets up its stack frame.

 * We need to ignore that one and record the parent. Since

 * the stack frame for the traced function wasn't set up yet,

 * the stack_trace wont see the parent. That needs to be added

 * manually to stack_dump_trace[] as the first element.

 */

#ifdef CC_USING_FENTRY

# define add_func	1

# define fentry		1

#else

# define add_func	0

# define fentry		0

#endif



static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =

	 { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };

static unsigned stack_dump_index[STACK_TRACE_ENTRIES];



/*

 * Reserve one entry for the passed in ip. This will allow

 * us to remove most or all of the stack size overhead

 * added by the stack tracer itself.

 */

static struct stack_trace max_stack_trace = {

	.max_entries		= STACK_TRACE_ENTRIES - add_func,

	.entries		= &stack_dump_trace[add_func],

	.max_entries		= STACK_TRACE_ENTRIES - 1,

	.entries		= &stack_dump_trace[1],

};



static unsigned long max_stack_size;
@@ -58,10 +55,14 @@ check_stack(unsigned long ip, unsigned long *stack) 
{

	unsigned long this_size, flags;

	unsigned long *p, *top, *start;

	static int tracer_frame;

	int frame_size = ACCESS_ONCE(tracer_frame);

	int i;



	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);

	this_size = THREAD_SIZE - this_size;

	/* Remove the frame of the tracer */

	this_size -= frame_size;



	if (this_size <= max_stack_size)

		return;
@@ -73,6 +74,10 @@ check_stack(unsigned long ip, unsigned long *stack) 
	local_irq_save(flags);

	arch_spin_lock(&max_stack_lock);



	/* In case another CPU set the tracer_frame on us */

	if (unlikely(!frame_size))

		this_size -= tracer_frame;



	/* a race could have already updated it */

	if (this_size <= max_stack_size)

		goto out;
@@ -85,15 +90,12 @@ check_stack(unsigned long ip, unsigned long *stack) 
	save_stack_trace(&max_stack_trace);



	/*

	 * When fentry is used, the traced function does not get

	 * its stack frame set up, and we lose the parent.

	 * Add that one in manally. We set up save_stack_trace()

	 * to not touch the first element in this case.

	 * Add the passed in ip from the function tracer.

	 * Searching for this on the stack will skip over

	 * most of the overhead from the stack tracer itself.

	 */

	if (add_func) {

	stack_dump_trace[0] = ip;

	max_stack_trace.nr_entries++;

	}



	/*

	 * Now find where in the stack these are.
@@ -123,6 +125,18 @@ check_stack(unsigned long ip, unsigned long *stack) 
				found = 1;

				/* Start the search from here */

				start = p + 1;

				/*

				 * We do not want to show the overhead

				 * of the stack tracer stack in the

				 * max stack. If we haven't figured

				 * out what that is, then figure it out

				 * now.

				 */

				if (unlikely(!tracer_frame) && i == 1) {

					tracer_frame = (p - stack) *

						sizeof(unsigned long);

					max_stack_size -= tracer_frame;

				}

			}

		}
@@ -149,7 +163,26 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip, 
	if (per_cpu(trace_active, cpu)++ != 0)

		goto out;



	check_stack(parent_ip, &stack);

	/*

	 * When fentry is used, the traced function does not get

	 * its stack frame set up, and we lose the parent.

	 * The ip is pretty useless because the function tracer

	 * was called before that function set up its stack frame.

	 * In this case, we use the parent ip.

	 *

	 * By adding the return address of either the parent ip

	 * or the current ip we can disregard most of the stack usage

	 * caused by the stack tracer itself.

	 *

	 * The function tracer always reports the address of where the

	 * mcount call was, but the stack will hold the return address.

	 */

	if (fentry)

		ip = parent_ip;

	else

		ip += MCOUNT_INSN_SIZE;



	check_stack(ip, &stack);



 out:

	per_cpu(trace_active, cpu)--;

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