Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=94c61c0aeffe64452e742087cf803d0347ef8418
Commit:     94c61c0aeffe64452e742087cf803d0347ef8418
Parent:     512e67f991c8886de75a65b854d7c19a55fb5b8a
Author:     Tim Pepper <[EMAIL PROTECTED]>
AuthorDate: Thu Oct 11 22:11:11 2007 +0200
Committer:  Peter Zijlstra <[EMAIL PROTECTED]>
CommitDate: Thu Oct 11 22:11:11 2007 +0200

    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 <[EMAIL PROTECTED]>
    Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
    Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
    Cc: Ingo Molnar <[EMAIL PROTECTED]>
    Cc: Al Viro <[EMAIL PROTECTED]>
---
 kernel/lockdep_proc.c |   61 +++++++++++++++++++++++++++++++++---------------
 1 files changed, 42 insertions(+), 19 deletions(-)

diff --git a/kernel/lockdep_proc.c b/kernel/lockdep_proc.c
index c851b2d..8a135bd 100644
--- 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;
 }
 
-
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