Re: [PATCH] async: fix insert entry in ascending list

[Vaughan Cao]

On 2013å12æ18æ 20:25, Tejun Heo wrote:
> Hello,
>
> On Wed, Dec 18, 2013 at 11:15:23AM +0800, Vaughan Cao wrote:
> > I suppose there is a fault in the patch of https://lkml.org/lkml/2013/1/16/546.
> > I know you made a new patch for latest kernel which don't move the entry
> > between pending and running list that remove the code I mentioned, but our
> > kernel is based on v3.8.13 that has the code.
> >
> > In my understanding, both pending and running list are sorted ascendingly by
> > cookie value. To find the correct postion to insert the entry into running
> > list, we traverse reversely to the head. When a node with a smaller cookie is
> > found, we break out and add the new entry after it. But the origin code tries
> > to find a larger cookie and insert itself before that node, it won't result in
> > a sorted list in any direction...
> Yeah, I should have used list_for_each_entry() there.  LOL, I'm an
> idiot.
I guess your original intention to use _reverse is that would take less 
steps to find the right position:)

> > I don't know if my understanding about the async mechanism is right, so here
> > to have a check with you. Thanks.
> >
> > Signed-off-by: Vaughan Cao <vaughan.cao@xxxxxxxxxx>
> > ---
> >   kernel/async.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/async.c b/kernel/async.c
> > index 6f34904..596c5e7 100644
> > --- a/kernel/async.c
> > +++ b/kernel/async.c
> > @@ -135,9 +135,9 @@ static void async_run_entry_fn(struct work_struct *work)
> >   	/* 1) move self to the running queue, make sure it stays sorted */
> >   	spin_lock_irqsave(&async_lock, flags);
> >   	list_for_each_entry_reverse(pos, &running->domain, list)
> > -		if (entry->cookie < pos->cookie)
> > +		if (entry->cookie > pos->cookie)
> >   			break;
> > -	list_move_tail(&entry->list, &pos->list);
> > +	list_move(&entry->list, &pos->list);
> Hmmm... sadly, upstream doesn't have the ability to backport this.
> The relevant code path is gone and -stable doesn't backport patches
> which aren't mainline first.  The only way would be backporting
> through distros, I guess.  But, again, this problem shouldn't be
> noticeable with modern userland and it has been broekn without anyone
> noticing for long enough, so maybe we can just leave it alone?
>
> Thanks.
Got it. I'll consider pulling your patch of leaving node in pending list 
into our kernel. Thanks.
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