Re: [PATCH for-next 15/16] RDMA/rxe: Add workqueue support for tasks

[Leon Romanovsky <leon@kernel.org>]

On Tue, Oct 18, 2022 at 10:18:13AM -0500, Bob Pearson wrote:
> On 10/18/22 03:59, Leon Romanovsky wrote:
> > On Mon, Oct 17, 2022 at 11:33:46PM -0500, Bob Pearson wrote:
> >> Add a third task type RXE_TASK_TYPE_WORKQUEUE to rxe_task.c.
> > 
> > Why do you need an extra type and not instead of RXE_TASK_TYPE_TASKLET?
> 
> It performs much better in some settings.
> > 
> >>
> >> Signed-off-by: Ian Ziemba <ian.ziemba@hpe.com>
> >> Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
> >> ---
> >>  drivers/infiniband/sw/rxe/rxe.c      |  9 ++-
> >>  drivers/infiniband/sw/rxe/rxe_task.c | 84 ++++++++++++++++++++++++++++
> >>  drivers/infiniband/sw/rxe/rxe_task.h | 10 +++-
> >>  3 files changed, 101 insertions(+), 2 deletions(-)

<...>

> >> +static void work_do_task(struct work_struct *work)
> >> +{
> >> +	struct rxe_task *task = container_of(work, typeof(*task), work);
> >> +
> >> +	if (!task->valid)
> >> +		return;
> > 
> > How can it be that submitted task is not valid? Especially without any
> > locking.
> 
> This and a similar subroutine for tasklets are called deferred and can have a significant
> delay before being called. In the mean time someone could have tried to destroy the QP. The valid
> flag is only cleared by QP destroy code and is not turned back on. Perhaps a rmb().

rmb() is not a locking.

> > 
> >> +
> >> +	do_task(task);
> >> +}
> > 
> > Thanks
> > 
> >> +
>