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Commit 94c61c0a authored by Tim Pepper's avatar Tim Pepper Committed by Peter Zijlstra
Browse files

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: default avatarTim Pepper <lnxninja@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Al Viro <viro@ftp.linux.org.uk>
parent 512e67f9

kernel/lockdep_proc.c

+42 −19
Original line number Diff line number Diff line
@@ -25,29 +25,39 @@ 


static void *l_next(struct seq_file *m, void *v, loff_t *pos)

{

	struct lock_class *class = v;

	struct lock_class *class;



	(*pos)++;



	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);

			class = list_entry(class->lock_entry.next,

					   struct lock_class, lock_entry);

		else

			class = NULL;

	m->private = class;

	}



	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;



	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)++;



	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;

}