linux-kernel - Re: [PATCH] llist: Don't reinvent the wheel but use existing llist API

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Date:   Mon, 13 Feb 2017 14:14:03 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     NeilBrown <neilb@...e.com>
Cc:     peterz@...radead.org, mingo@...nel.org, koverstreet@...gle.com,
        neilb@...e.de, nab@...ux-iscsi.org, viro@...iv.linux.org.uk,
        ying.huang@...el.com, oleg@...hat.com, asias@...hat.com,
        shli@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] llist: Don't reinvent the wheel but use existing llist
 API

On Mon, Feb 13, 2017 at 03:56:08PM +1100, NeilBrown wrote:
> On Mon, Feb 13 2017, Byungchul Park wrote:
> 
> > Although llist provides proper APIs, they are not used. Make them used.
> >
> > Signed-off-by: Byungchul Park <byungchul.park@....com>
> > ---
> >  drivers/md/bcache/closure.c | 15 ++-------------
> >  drivers/md/raid5.c          |  4 +---
> >  drivers/vhost/scsi.c        |  9 ++-------
> >  fs/file_table.c             | 12 +++++-------
> >  fs/namespace.c              | 12 +++++-------
> >  include/linux/llist.h       |  3 +++
> >  kernel/irq_work.c           |  6 +-----
> >  kernel/sched/core.c         | 13 ++-----------
> >  mm/vmalloc.c                |  8 +++-----
> >  9 files changed, 24 insertions(+), 58 deletions(-)
> >
> ...
> 
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index 36c13e4..c82243a 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -359,11 +359,9 @@ static int release_stripe_list(struct r5conf *conf,
> >  
> >  	head = llist_del_all(&conf->released_stripes);
> >  	head = llist_reverse_order(head);
> > -	while (head) {
> > +	llist_for_each_entry(sh, head, release_list) {
> >  		int hash;
> >  
> > -		sh = llist_entry(head, struct stripe_head, release_list);
> > -		head = llist_next(head);
> >  		/* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */
> >  		smp_mb();
> >  		clear_bit(STRIPE_ON_RELEASE_LIST, &sh->state);
> 
> This one is wrong (I haven't checked the rest).
> As soon a STRIPE_ON_RELEASE_LIST is cleared, the llist_node can be
> reused, so we need to call llist_next *before* the rest of the code.
> You have moved the call to afterwards.
> 
> You could possibly change it to use llist_for_each_entry_safe()

Yes right. I also found that I should have used the safe version. :(

Thank you very much.

> 
> NeilBrown