Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference()

[Patrick Marlier]

On 10/28/2015 09:33 AM, Ingo Molnar wrote:
> * Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> > Subject: writeback: don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs()
> >
> > bdi_split_work_to_wbs() uses list_for_each_entry_rcu_continue() to
> > walk @bdi->wb_list.  To set up the initial iteration condition, it
> > uses list_entry_rcu() to calculate the entry pointer corresponding to
> > the list head; however, this isn't an actual RCU dereference and using
> > list_entry_rcu() for it ended up breaking a proposed list_entry_rcu()
> > change because it was feeding an non-lvalue pointer into the macro.
> >
> > Don't use the RCU variant for simple pointer offsetting.  Use
> > list_entry() instead.
> >
> > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> > ---
> >   fs/fs-writeback.c |    4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 29e4599..7378169 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -779,8 +779,8 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
> >   				  bool skip_if_busy)
> >   {
> >   	struct bdi_writeback *last_wb = NULL;
> > -	struct bdi_writeback *wb = list_entry_rcu(&bdi->wb_list,
> > -						struct bdi_writeback, bdi_node);
> > +	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
> > +					      struct bdi_writeback, bdi_node);
> >
> >   	might_sleep();
>
> Any objections against me applying this fix to tip:core/rcu so that I can push the
> recent RCU changes towards linux-next without triggering a build failure?

No objection on my side but probably you are waiting for an ack from 
somebody else.
--
Pat
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