ftrace: stack trace add indexes

This patch adds indexes into the stack that the functions in the
stack dump were found at. As an added bonus, I also added a diff
to show which function is the most notorious consumer of the stack.

The output now looks like this:

# cat /debug/tracing/stack_trace
        Depth   Size      Location    (48 entries)
        -----   ----      --------
  0)     2476     212   blk_recount_segments+0x39/0x59
  1)     2264      12   bio_phys_segments+0x16/0x1d
  2)     2252      20   blk_rq_bio_prep+0x23/0xaf
  3)     2232      12   init_request_from_bio+0x74/0x77
  4)     2220      56   __make_request+0x294/0x331
  5)     2164     136   generic_make_request+0x34f/0x37d
  6)     2028      56   submit_bio+0xe7/0xef
  7)     1972      28   submit_bh+0xd1/0xf0
  8)     1944     112   block_read_full_page+0x299/0x2a9
  9)     1832       8   blkdev_readpage+0x14/0x16
 10)     1824      28   read_cache_page_async+0x7e/0x109
 11)     1796      16   read_cache_page+0x11/0x49
 12)     1780      32   read_dev_sector+0x3c/0x72
 13)     1748      48   read_lba+0x4d/0xaa
 14)     1700     168   efi_partition+0x85/0x61b
 15)     1532      72   rescan_partitions+0x10e/0x266
 16)     1460      40   do_open+0x1c7/0x24e
 17)     1420     292   __blkdev_get+0x79/0x84
 18)     1128      12   blkdev_get+0x12/0x14
 19)     1116      20   register_disk+0xd1/0x11e
 20)     1096      28   add_disk+0x34/0x90
 21)     1068      52   sd_probe+0x2b1/0x366
 22)     1016      20   driver_probe_device+0xa5/0x120
 23)      996       8   __device_attach+0xd/0xf
 24)      988      32   bus_for_each_drv+0x3e/0x68
 25)      956      24   device_attach+0x56/0x6c
 26)      932      16   bus_attach_device+0x26/0x4d
 27)      916      64   device_add+0x380/0x4b4
 28)      852      28   scsi_sysfs_add_sdev+0xa1/0x1c9
 29)      824     160   scsi_probe_and_add_lun+0x919/0xa2a
 30)      664      36   __scsi_add_device+0x88/0xae
 31)      628      44   ata_scsi_scan_host+0x9e/0x21c
 32)      584      28   ata_host_register+0x1cb/0x1db
 33)      556      24   ata_host_activate+0x98/0xb5
 34)      532     192   ahci_init_one+0x9bd/0x9e9
 35)      340      20   pci_device_probe+0x3e/0x5e
 36)      320      20   driver_probe_device+0xa5/0x120
 37)      300      20   __driver_attach+0x3f/0x5e
 38)      280      36   bus_for_each_dev+0x40/0x62
 39)      244      12   driver_attach+0x19/0x1b
 40)      232      28   bus_add_driver+0x9c/0x1af
 41)      204      28   driver_register+0x76/0xd2
 42)      176      20   __pci_register_driver+0x44/0x71
 43)      156       8   ahci_init+0x14/0x16
 44)      148     100   _stext+0x42/0x122
 45)       48      20   kernel_init+0x175/0x1dc
 46)       28      28   kernel_thread_helper+0x7/0x10

The first column is simply an index starting from the inner most function
and counting down to the outer most.

The next column is the location that the function was found on the stack.

The next column is the size of the stack for that function.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_stack.c

@@ -16,8 +16,10 @@
 
 #define STACK_TRACE_ENTRIES 500
 
-static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES] =
-	{ [0 ... (STACK_TRACE_ENTRIES-1)] = ULONG_MAX };
+static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
+	 { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
+static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
+
 static struct stack_trace max_stack_trace = {
 	.max_entries		= STACK_TRACE_ENTRIES,
 	.entries		= stack_dump_trace,
@@ -32,8 +34,9 @@ static DEFINE_PER_CPU(int, trace_active);
 
 static inline void check_stack(void)
 {
-	unsigned long this_size;
-	unsigned long flags;
+	unsigned long this_size, flags;
+	unsigned long *p, *top, *start;
+	int i;
 
 	this_size = ((unsigned long)&this_size) & (THREAD_SIZE-1);
 	this_size = THREAD_SIZE - this_size;
@@ -51,10 +54,42 @@ static inline void check_stack(void)
 	max_stack_size = this_size;
 
 	max_stack_trace.nr_entries	= 0;
-	max_stack_trace.skip		= 1;
+	max_stack_trace.skip		= 3;
 
 	save_stack_trace(&max_stack_trace);
 
+	/*
+	 * Now find where in the stack these are.
+	 */
+	i = 0;
+	start = &this_size;
+	top = (unsigned long *)
+		(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
+
+	/*
+	 * Loop through all the entries. One of the entries may
+	 * for some reason be missed on the stack, so we may
+	 * have to account for them. If they are all there, this
+	 * loop will only happen once. This code only takes place
+	 * on a new max, so it is far from a fast path.
+	 */
+	while (i < max_stack_trace.nr_entries) {
+
+		stack_dump_index[i] = this_size;
+		p = start;
+
+		for (; p < top && i < max_stack_trace.nr_entries; p++) {
+			if (*p == stack_dump_trace[i]) {
+				this_size = stack_dump_index[i++] =
+					(top - p) * sizeof(unsigned long);
+				/* Start the search from here */
+				start = p + 1;
+			}
+		}
+
+		i++;
+	}
+
  out:
 	__raw_spin_unlock(&max_stack_lock);
 	raw_local_irq_restore(flags);
@@ -145,22 +180,24 @@ static struct file_operations stack_max_size_fops = {
 static void *
 t_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	unsigned long *t = m->private;
+	long i = (long)m->private;
 
 	(*pos)++;
 
-	if (!t || *t == ULONG_MAX)
+	i++;
+
+	if (i >= max_stack_trace.nr_entries ||
+	    stack_dump_trace[i] == ULONG_MAX)
 		return NULL;
 
-	t++;
-	m->private = t;
+	m->private = (void *)i;
 
-	return t;
+	return &m->private;
 }
 
 static void *t_start(struct seq_file *m, loff_t *pos)
 {
-	unsigned long *t = m->private;
+	void *t = &m->private;
 	loff_t l = 0;
 
 	local_irq_disable();
@@ -178,14 +215,15 @@ static void t_stop(struct seq_file *m, void *p)
 	local_irq_enable();
 }
 
-static int trace_lookup_stack(struct seq_file *m, unsigned long addr)
+static int trace_lookup_stack(struct seq_file *m, long i)
 {
+	unsigned long addr = stack_dump_trace[i];
 #ifdef CONFIG_KALLSYMS
 	char str[KSYM_SYMBOL_LEN];
 
 	sprint_symbol(str, addr);
 
-	return seq_printf(m, "[<%p>] %s\n", (void*)addr, str);
+	return seq_printf(m, "%s\n", str);
 #else
 	return seq_printf(m, "%p\n", (void*)addr);
 #endif
@@ -193,12 +231,30 @@ static int trace_lookup_stack(struct seq_file *m, unsigned long addr)
 
 static int t_show(struct seq_file *m, void *v)
 {
-	unsigned long *t = v;
+	long i = *(long *)v;
+	int size;
+
+	if (i < 0) {
+		seq_printf(m, "        Depth   Size      Location"
+			   "    (%d entries)\n"
+			   "        -----   ----      --------\n",
+			   max_stack_trace.nr_entries);
+		return 0;
+	}
 
-	if (!t || *t == ULONG_MAX)
+	if (i >= max_stack_trace.nr_entries ||
+	    stack_dump_trace[i] == ULONG_MAX)
 		return 0;
 
-	trace_lookup_stack(m, *t);
+	if (i+1 == max_stack_trace.nr_entries ||
+	    stack_dump_trace[i+1] == ULONG_MAX)
+		size = stack_dump_index[i];
+	else
+		size = stack_dump_index[i] - stack_dump_index[i+1];
+
+	seq_printf(m, "%3ld) %8d   %5d   ", i, stack_dump_index[i], size);
+
+	trace_lookup_stack(m, i);
 
 	return 0;
 }
@@ -217,7 +273,7 @@ static int stack_trace_open(struct inode *inode, struct file *file)
 	ret = seq_open(file, &stack_trace_seq_ops);
 	if (!ret) {
 		struct seq_file *m = file->private_data;
-		m->private = stack_dump_trace;
+		m->private = (void *)-1;
 	}
 
 	return ret;