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.
Signed-off-by: Tim Pepper <lnxninja@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
---
Assuming people are fine with this, it should probably find its way
to stable.
If you haven't seen the infinite output: it's easy to trigger with a
simple 'cat /proc/lockdep' generally for me, a cat /proc/lock_stat piped
to a file or for either of them a dd with the default bs=512 (or smaller)
should do the job also.
With this change to the lock_stat handler the data->iter member no longer
attempts to hold state across calls, so it could be taken out of the
lock_stat_seq struct and replace by a local variable in each function
but that isn't a clear win to me so I just left it.
--- linux-2.6.23-rc9.orig/kernel/lockdep_proc.c
+++ linux-2.6.23-rc9/kernel/lockdep_proc.c
@@ -34,19 +34,23 @@ static void *l_next(struct seq_file *m,
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)
+ if (*pos == 0)
seq_printf(m, "all lock classes:\n");
+ list_for_each_entry(class, &all_lock_classes, lock_entry) {
+ if (i++ == *pos)
+ return class;
+ }
+ return NULL;
- return class;
}
static void l_stop(struct seq_file *m, void *v)
@@ -101,7 +105,7 @@ static void print_name(struct seq_file *
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;
@@ -523,12 +527,15 @@ static void *ls_start(struct seq_file *m
{
struct lock_stat_seq *data = m->private;
- if (data->iter == data->stats)
- seq_header(m);
+ data->iter = data->stats;
+ data->iter += *pos;
- if (data->iter == data->iter_end)
+ if (data->iter >= data->iter_end)
data->iter = NULL;
+ if (data->iter == data->stats)
+ seq_header(m);
+
return data->iter;
}
-
