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 <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
---
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;
}
On Mon, Oct 08, 2007 at 06:15:51PM -0700, Tim Pepper wrote:
>
> 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.
>
> 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");
Do not generate output outside of ->show() and you won't have these
problems. That's where your infinite output crap comes from.
IOW, NAK - fix the underlying problem.
On Tue 09 Oct at 02:30:11 +0100 [email protected] said:
> On Mon, Oct 08, 2007 at 06:15:51PM -0700, Tim Pepper wrote:
> >
> > - if (&class->lock_entry == all_lock_classes.next)
> > + if (*pos == 0)
> > seq_printf(m, "all lock classes:\n");
>
> Do not generate output outside of ->show() and you won't have these
> problems. That's where your infinite output crap comes from.
>
> IOW, NAK - fix the underlying problem.
Aaah...OK. Can we add something like the following then:
Document that output must only come from _show() and SEQ_START_TOKEN is how
a _start() indicates a header is to be printed.
Signed-off-by: Tim Pepper <[email protected]>
Cc: Al Viro <[email protected]>
---
--- linux-2.6.orig/include/linux/seq_file.h
+++ linux-2.6.23-rc9/include/linux/seq_file.h
@@ -36,9 +36,10 @@ ssize_t seq_read(struct file *, char __u
loff_t seq_lseek(struct file *, loff_t, int);
int seq_release(struct inode *, struct file *);
int seq_escape(struct seq_file *, const char *, const char *);
+
+/* these may only be called from a (*show) function */
int seq_putc(struct seq_file *m, char c);
int seq_puts(struct seq_file *m, const char *s);
-
int seq_printf(struct seq_file *, const char *, ...)
__attribute__ ((format (printf,2,3)));
@@ -48,6 +49,11 @@ int single_open(struct file *, int (*)(s
int single_release(struct inode *, struct file *);
int seq_release_private(struct inode *, struct file *);
+/*
+ * return SEQ_START_TOKEN in your (*start) function and test for
+ * (v == SEQ_START_TOKEN) in * your (*show) funtion in order to
+ * print a header before your seq data
+ */
#define SEQ_START_TOKEN ((void *)1)
/*
On Tue, 2007-10-09 at 02:30 +0100, Al Viro wrote:
> On Mon, Oct 08, 2007 at 06:15:51PM -0700, Tim Pepper wrote:
> >
> > 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.
> >
> > 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");
>
> Do not generate output outside of ->show() and you won't have these
> problems. That's where your infinite output crap comes from.
>
> IOW, NAK - fix the underlying problem.
FWIW I had to do Tim's bits too. Just moving all output from the start
into the show method didn't fix it.
Signed-off-by: Tim Pepper <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
---
kernel/lockdep_proc.c | 69 +++++++++++++++++++++++---------------------------
1 file changed, 33 insertions(+), 36 deletions(-)
Index: linux-2.6/kernel/lockdep_proc.c
===================================================================
--- linux-2.6.orig/kernel/lockdep_proc.c
+++ linux-2.6/kernel/lockdep_proc.c
@@ -23,32 +23,25 @@
#include "lockdep_internals.h"
-static void *l_next(struct seq_file *m, void *v, loff_t *pos)
+static void *l_start(struct seq_file *m, loff_t *pos)
{
- struct lock_class *class = v;
-
- (*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;
+ struct lock_class *class;
+ int i = 0;
- return class;
+ list_for_each_entry(class, &all_lock_classes, lock_entry) {
+ if (i++ == *pos)
+ return class;
+ }
+ return NULL;
}
-static void *l_start(struct seq_file *m, loff_t *pos)
+static void *l_next(struct seq_file *m, void *v, loff_t *pos)
{
- struct lock_class *class = m->private;
-
- if (&class->lock_entry == all_lock_classes.next)
- seq_printf(m, "all lock classes:\n");
-
- return class;
+ (*pos)++;
+ return l_start(m, pos);
}
+
static void l_stop(struct seq_file *m, void *v)
{
}
@@ -101,10 +94,16 @@ 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;
+ if (WARN_ON(class == NULL))
+ return 0;
+
+ if (&class->lock_entry == all_lock_classes.next)
+ seq_printf(m, "all lock classes:\n");
+
seq_printf(m, "%p", class->key);
#ifdef CONFIG_DEBUG_LOCKDEP
seq_printf(m, " OPS:%8ld", class->ops);
@@ -522,28 +521,19 @@ static void seq_header(struct seq_file *
static void *ls_start(struct seq_file *m, loff_t *pos)
{
struct lock_stat_seq *data = m->private;
+ struct lock_stat_data *iter;
- if (data->iter == data->stats)
- seq_header(m);
-
- if (data->iter == data->iter_end)
- data->iter = NULL;
+ iter = data->iter + *pos;
+ if (iter >= data->iter_end)
+ iter = NULL;
- return data->iter;
+ return iter;
}
static void *ls_next(struct seq_file *m, void *v, loff_t *pos)
{
- struct lock_stat_seq *data = m->private;
-
(*pos)++;
-
- data->iter = v;
- data->iter++;
- if (data->iter == data->iter_end)
- data->iter = NULL;
-
- return data->iter;
+ return ls_start(m, pos);
}
static void ls_stop(struct seq_file *m, void *v)
@@ -553,8 +543,15 @@ static void ls_stop(struct seq_file *m,
static int ls_show(struct seq_file *m, void *v)
{
struct lock_stat_seq *data = m->private;
+ struct lock_stat_data *iter = v;
+
+ if (WARN_ON(iter == NULL))
+ return 0;
+
+ if (iter == data->iter)
+ seq_header(m);
- seq_stats(m, data->iter);
+ seq_stats(m, iter);
return 0;
}
On Tue 09 Oct at 13:14:49 +0200 [email protected] said:
> FWIW I had to do Tim's bits too. Just moving all output from the start
> into the show method didn't fix it.
Yes. The way the original lockdep_proc.c code was doing its pointers
around its seq data was definitely wrong, regardless of the output
outside of _show().
> -static void *l_start(struct seq_file *m, loff_t *pos)
> +static void *l_next(struct seq_file *m, void *v, loff_t *pos)
> {
> - struct lock_class *class = m->private;
> -
> - if (&class->lock_entry == all_lock_classes.next)
> - seq_printf(m, "all lock classes:\n");
> -
> - return class;
> + (*pos)++;
> + return l_start(m, pos);
> }
Isn't this is going to make l_start/l_next() approach O(n^2) when they can
be more like O(n)? It appears to be the case that _next() will always
get a valid *v, so you can just step immediately to the next element.
The _start() seems to be the only place where you'd actually need to
search based on *pos.
The below moves the headers out of the _start() functions, but by using
SEQ_START_TOKEN (as appears to be the trend in other seq_file users)
to differentiate. This means *pos==0 then is the header and *pos==1..n
are the lock class elements 0..(n-1), which again appears to be what
others are doing.
================================================================
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 <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Al Viro <[email protected]>
---
Compared to my previous version this now also has output only happening
in _show(). Compared to Peter's version with output only in _show(),
this is more efficient in its _next().
--- linux-2.6.23-rc9.orig/kernel/lockdep_proc.c
+++ linux-2.6.23-rc9/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 (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;
+ }
- 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;
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;
- return class;
}
static void l_stop(struct seq_file *m, void *v)
@@ -101,10 +111,15 @@ 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;
+ 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
{
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,
(*pos)++;
+ if (v == SEQ_START_TOKEN)
+ data->iter = data->stats;
+ else {
+ data->iter = v;
+ data->iter++;
+ }
+
- 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,
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;
}