Eric Lee / linux-smarc-t335x-v3.2

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Commit 94c61c0aeffe64452e742087cf803d0347ef8418

Authored by Tim Pepper
Committed by Peter Zijlstra
1 parent 512e67f991
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

lockdep: Avoid /proc/lockdep & lock_stat infinite output 

Both /proc/lockdep and /proc/lock_stat output may loop infinitely.

When a read() requests an amount of data smaller than the amount of data
that the seq_file's foo_show() outputs, the output starts looping and
outputs the "stuck" element's data infinitely.  There may be multiple
sequential calls to foo_start(), foo_next()/foo_show(), and foo_stop()
for a single open with sequential read of the file.  The _start() does not
have to start with the 0th element and _show() might be called multiple
times in a row for the same element for a given open/read of the seq_file.

Also header output should not be happening in _start().  All output should
be in _show(), which SEQ_START_TOKEN is meant to help.  Having output in
_start() may also negatively impact seq_file's seq_read() and traverse()
accounting.

Signed-off-by: Tim Pepper <lnxninja@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Al Viro <viro@ftp.linux.org.uk>

Showing 1 changed file with 42 additions and 19 deletions Side-by-side Diff

kernel/lockdep_proc.c
Diff comments   View file @ 94c61c0
... ... @@ -25,28 +25,38 @@
25 25  
26 26 static void *l_next(struct seq_file *m, void *v, loff_t *pos)
27 27 {
28   - struct lock_class *class = v;
  28 + struct lock_class *class;
29 29  
30 30 (*pos)++;
31 31  
32   - if (class->lock_entry.next != &all_lock_classes)
33   - class = list_entry(class->lock_entry.next, struct lock_class,
34   - lock_entry);
35   - else
36   - class = NULL;
37   - m->private = class;
  32 + if (v == SEQ_START_TOKEN)
  33 + class = m->private;
  34 + else {
  35 + class = v;
38 36  
  37 + if (class->lock_entry.next != &all_lock_classes)
  38 + class = list_entry(class->lock_entry.next,
  39 + struct lock_class, lock_entry);
  40 + else
  41 + class = NULL;
  42 + }
  43 +
39 44 return class;
40 45 }
41 46  
42 47 static void *l_start(struct seq_file *m, loff_t *pos)
43 48 {
44   - struct lock_class *class = m->private;
  49 + struct lock_class *class;
  50 + loff_t i = 0;
45 51  
46   - if (&class->lock_entry == all_lock_classes.next)
47   - seq_printf(m, "all lock classes:\n");
  52 + if (*pos == 0)
  53 + return SEQ_START_TOKEN;
48 54  
49   - return class;
  55 + list_for_each_entry(class, &all_lock_classes, lock_entry) {
  56 + if (++i == *pos)
  57 + return class;
  58 + }
  59 + return NULL;
50 60 }
51 61  
52 62 static void l_stop(struct seq_file *m, void *v)
53 63  
... ... @@ -101,10 +111,15 @@
101 111 static int l_show(struct seq_file *m, void *v)
102 112 {
103 113 unsigned long nr_forward_deps, nr_backward_deps;
104   - struct lock_class *class = m->private;
  114 + struct lock_class *class = v;
105 115 struct lock_list *entry;
106 116 char c1, c2, c3, c4;
107 117  
  118 + if (v == SEQ_START_TOKEN) {
  119 + seq_printf(m, "all lock classes:\n");
  120 + return 0;
  121 + }
  122 +
108 123 seq_printf(m, "%p", class->key);
109 124 #ifdef CONFIG_DEBUG_LOCKDEP
110 125 seq_printf(m, " OPS:%8ld", class->ops);
111 126  
... ... @@ -523,10 +538,11 @@
523 538 {
524 539 struct lock_stat_seq *data = m->private;
525 540  
526   - if (data->iter == data->stats)
527   - seq_header(m);
  541 + if (*pos == 0)
  542 + return SEQ_START_TOKEN;
528 543  
529   - if (data->iter == data->iter_end)
  544 + data->iter = data->stats + *pos;
  545 + if (data->iter >= data->iter_end)
530 546 data->iter = NULL;
531 547  
532 548 return data->iter;
... ... @@ -538,8 +554,13 @@
538 554  
539 555 (*pos)++;
540 556  
541   - data->iter = v;
542   - data->iter++;
  557 + if (v == SEQ_START_TOKEN)
  558 + data->iter = data->stats;
  559 + else {
  560 + data->iter = v;
  561 + data->iter++;
  562 + }
  563 +
543 564 if (data->iter == data->iter_end)
544 565 data->iter = NULL;
545 566  
546 567  
... ... @@ -552,9 +573,11 @@
552 573  
553 574 static int ls_show(struct seq_file *m, void *v)
554 575 {
555   - struct lock_stat_seq *data = m->private;
  576 + if (v == SEQ_START_TOKEN)
  577 + seq_header(m);
  578 + else
  579 + seq_stats(m, v);
556 580  
557   - seq_stats(m, data->iter);
558 581 return 0;
559 582 }
560 583