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>

diff --git a/kernel/lockdep_proc.c b/kernel/lockdep_proc.c
index c851b2dcc685cc91db6bf16838aaab556517878e..8a135bd163c2cc719b4635b1e511aa87039d6f46 100644 (file)
--- a/kernel/lockdep_proc.c
+++ b/kernel/lockdep_proc.c
@@ -25,28 +25,38 @@
 
 static void *l_next(struct seq_file *m, void *v, loff_t *pos)
 {
-       struct lock_class *class = v;
+       struct lock_class *class;
 
        (*pos)++;
 
-       if (class->lock_entry.next != &all_lock_classes)
-               class = list_entry(class->lock_entry.next, struct lock_class,
-                                 lock_entry);
-       else
-               class = NULL;
-       m->private = class;
+       if (v == SEQ_START_TOKEN)
+               class = m->private;
+       else {
+               class = v;
+
+               if (class->lock_entry.next != &all_lock_classes)
+                       class = list_entry(class->lock_entry.next,
+                                          struct lock_class, lock_entry);
+               else
+                       class = NULL;
+       }
 
        return class;
 }
 
 static void *l_start(struct seq_file *m, loff_t *pos)
 {
-       struct lock_class *class = m->private;
+       struct lock_class *class;
+       loff_t i = 0;
 
-       if (&class->lock_entry == all_lock_classes.next)
-               seq_printf(m, "all lock classes:\n");
+       if (*pos == 0)
+               return SEQ_START_TOKEN;
 
-       return class;
+       list_for_each_entry(class, &all_lock_classes, lock_entry) {
+               if (++i == *pos)
+               return class;
+       }
+       return NULL;
 }
 
 static void l_stop(struct seq_file *m, void *v)
@@ -101,10 +111,15 @@ static void print_name(struct seq_file *m, struct lock_class *class)
 static int l_show(struct seq_file *m, void *v)
 {
        unsigned long nr_forward_deps, nr_backward_deps;
-       struct lock_class *class = m->private;
+       struct lock_class *class = v;
        struct lock_list *entry;
        char c1, c2, c3, c4;
 
+       if (v == SEQ_START_TOKEN) {
+               seq_printf(m, "all lock classes:\n");
+               return 0;
+       }
+
        seq_printf(m, "%p", class->key);
 #ifdef CONFIG_DEBUG_LOCKDEP
        seq_printf(m, " OPS:%8ld", class->ops);
@@ -523,10 +538,11 @@ static void *ls_start(struct seq_file *m, loff_t *pos)
 {
        struct lock_stat_seq *data = m->private;
 
-       if (data->iter == data->stats)
-               seq_header(m);
+       if (*pos == 0)
+               return SEQ_START_TOKEN;
 
-       if (data->iter == data->iter_end)
+       data->iter = data->stats + *pos;
+       if (data->iter >= data->iter_end)
                data->iter = NULL;
 
        return data->iter;
@@ -538,8 +554,13 @@ static void *ls_next(struct seq_file *m, void *v, loff_t *pos)
 
        (*pos)++;
 
-       data->iter = v;
-       data->iter++;
+       if (v == SEQ_START_TOKEN)
+               data->iter = data->stats;
+       else {
+               data->iter = v;
+               data->iter++;
+       }
+
        if (data->iter == data->iter_end)
                data->iter = NULL;
 
@@ -552,9 +573,11 @@ static void ls_stop(struct seq_file *m, void *v)
 
 static int ls_show(struct seq_file *m, void *v)
 {
-       struct lock_stat_seq *data = m->private;
+       if (v == SEQ_START_TOKEN)
+               seq_header(m);
+       else
+               seq_stats(m, v);
 
-       seq_stats(m, data->iter);
        return 0;
 }