Andrew Morton wrote:
> On Wed, 03 Sep 2008 18:27:12 +0200 Tejun Heo <tj@xxxxxxxxxx> wrote:
>
>> Andrew Morton wrote:
>>> @@ -674,6 +674,8 @@ static void *disk_seqf_next(struct seq_f
>>> struct device *dev;
>>>
>>> (*pos)++;
>>> + if (seqf->private == NULL)
>>> + return NULL;
>>> dev = class_dev_iter_next(seqf->private);
>>> if (dev)
>>> return dev_to_disk(dev);
>> Ehh... next can't be called with NULL private.
>
> My computer disagreed ;)
>
>> Where can I take a look
>> at the merged tree? There have been two separate changes to that area
>> of code. Ad-hoc behavior fix for 2.6.27 and general clean up scheduled
>> for 2.6.28 and the two use seqf->private for different purposes. Maybe
>> the two got mixed up?
>
> It's linux-next-20080903
Hmmm... Can't see how it can happen and can't reproduce it either.
seqf->private is initialized from disk_seqf_start(). If allocation
fails, it returns ERR_PTR(-ENOMEM). On error return from start, both
seq_file::seq_read and seq_file::traverse() immediately calls ->stop()
and fails, so ->next can't really be called with null ->private.
Just to make sure, I made disk_seqf_start() fail and it works (or
rather fails) as expected.
Argggghh... strange. Can you please try the attached patch and post
the log?
Thanks.
--
tejun
diff --git a/block/genhd.c b/block/genhd.c
index ed926b7..b76c56b 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -655,8 +655,11 @@ static void *disk_seqf_start(struct seq_file *seqf, loff_t *pos)
struct device *dev;
iter = kmalloc(sizeof(*iter), GFP_KERNEL);
- if (!iter)
+ if (!iter) {
+ printk("XXX disk_seqf_start: -ENOMEM\n");
return ERR_PTR(-ENOMEM);
+ }
+ printk("XXX disk_seqf_start: iter=%p pos=%lld\n", iter, (long long)*pos);
seqf->private = iter;
class_dev_iter_init(iter, &block_class, NULL, &disk_type);
@@ -673,6 +676,8 @@ static void *disk_seqf_next(struct seq_file *seqf, void *v, loff_t *pos)
{
struct device *dev;
+ printk("XXX disk_seqf_next: iter=%p pos=%lld\n",
+ seqf->private, (long long)*pos);
(*pos)++;
dev = class_dev_iter_next(seqf->private);
if (dev)
@@ -685,6 +690,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
{
struct class_dev_iter *iter = seqf->private;
+ printk("XXX disk_seqf_stop: iter=%p\n", seqf->private);
/* stop is called even after start failed :-( */
if (iter) {
class_dev_iter_exit(iter);
@@ -697,7 +703,7 @@ static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
static void *p;
p = disk_seqf_start(seqf, pos);
- if (!IS_ERR(p) && p)
+ if (!IS_ERR(p) && p && !*pos)
seq_puts(seqf, "major minor #blocks name\n\n");
return p;
}
