Re: [PATCH] RDMA/uverbs: Make the event_queue fds return POLLERR when disassociated

[Leon Romanovsky <leon@kernel.org>]

On Tue, Apr 07, 2020 at 08:51:15AM -0300, Jason Gunthorpe wrote:
> On Tue, Apr 07, 2020 at 08:16:32AM +0300, Leon Romanovsky wrote:
> > On Mon, Apr 06, 2020 at 09:44:26PM -0300, Jason Gunthorpe wrote:
> > > From: Jason Gunthorpe <jgg@mellanox.com>
> > >
> > > If is_closed is set, and the event list is empty, then read() will return
> > > -EIO without blocking. After setting is_closed in
> > > ib_uverbs_free_event_queue(), we do trigger a wake_up on the poll_wait,
> > > but the fops->poll() function does not check it, so poll will continue to
> > > sleep on an empty list.
> > >
> > > Fixes: 14e23bd6d221 ("RDMA/core: Fix locking in ib_uverbs_event_read")
> > > Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> > >  drivers/infiniband/core/uverbs_main.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
> > > index 2d4083bf4a0487..8710a3427146e7 100644
> > > +++ b/drivers/infiniband/core/uverbs_main.c
> > > @@ -296,6 +296,8 @@ static __poll_t ib_uverbs_event_poll(struct ib_uverbs_event_queue *ev_queue,
> > >  	spin_lock_irq(&ev_queue->lock);
> > >  	if (!list_empty(&ev_queue->event_list))
> > >  		pollflags = EPOLLIN | EPOLLRDNORM;
> > > +	else if (ev_queue->is_closed)
> > > +		pollflags = EPOLLERR;
> > >  	spin_unlock_irq(&ev_queue->lock);
> >
> > Don't you need to set EPOLLHUP too? Probably, it won't change anything,
> > just for the sake of the correctness.
>
> HUP means read will return 0, in this case read returns -EIO

I see, it is because we don't have events to read.

Thanks

>
> Jason