linux-kernel - Re: [PATCH v2 13/14] RDMA/rxe: Rename kfree_rcu() to kvfree_rcu

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Date:   Wed, 15 Mar 2023 15:59:54 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Bob Pearson <rpearsonhpe@...il.com>
Cc:     Zhu Yanjun <zyjzyj2000@...il.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        Devesh Sharma <devesh.s.sharma@...cle.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Zhu Yanjun <yanjun.zhu@...ux.dev>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 13/14] RDMA/rxe: Rename kfree_rcu() to kvfree_rcu_mightsleep()

On Wed, Mar 15, 2023 at 3:05 PM Bob Pearson <rpearsonhpe@...il.com> wrote:
>
> On 3/15/23 13:41, Joel Fernandes wrote:
> > On Wed, Mar 15, 2023 at 2:38 PM Bob Pearson <rpearsonhpe@...il.com> wrote:
> >>
> >> On 3/15/23 13:19, Joel Fernandes (Google) wrote:
> >>> The k[v]free_rcu() macro's single-argument form is deprecated.
> >>> Therefore switch to the new k[v]free_rcu_mightsleep() variant. The goal
> >>> is to avoid accidental use of the single-argument forms, which can
> >>> introduce functionality bugs in atomic contexts and latency bugs in
> >>> non-atomic contexts.
> >>>
> >>> There is no functionality change with this patch.
> >>>
> >>> Link: https://lore.kernel.org/rcu/20230201150815.409582-1-urezki@gmail.com
> >>> Acked-by: Zhu Yanjun <zyjzyj2000@...il.com>
> >>> Reviewed-by: Bob Pearson <rpearsonhpe@...il.com>
> >>> Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
> >>> Fixes: 72a03627443d ("RDMA/rxe: Remove rxe_alloc()")
> >>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> >>> ---
> >>>  drivers/infiniband/sw/rxe/rxe_mr.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
> >>> index b10aa1580a64..ae3a100e18fb 100644
> >>> --- a/drivers/infiniband/sw/rxe/rxe_mr.c
> >>> +++ b/drivers/infiniband/sw/rxe/rxe_mr.c
> >>> @@ -731,7 +731,7 @@ int rxe_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)
> >>>               return -EINVAL;
> >>>
> >>>       rxe_cleanup(mr);
> >>> -     kfree_rcu(mr);
> >>> +     kfree_rcu_mightsleep(mr);
> >>>       return 0;
> >>>  }
> >>>
> >> Please replace kfree_rcu_mightsleep() by kfree(). There is no need to delay the kfree(mr).
> >
> > I thought you said either was Ok, but yeah that's fine with me. I was
> > trying to play it safe ;-). An extra GP may not hurt, but not having
> > one when it is needed might. I will update it to just be kfree.
>
> Thanks. The reason to not add the pause is that it really isn't required and will just make
> people think that it is. With the current state of the driver the mr cleanup code will disable
> looking up the mr from its rkey or lkey and then wait until all the references to the mr are dropped
> before calling kfree. This will always work (unless a new bug is introduced) so no reason to
> add the rcu delay.
>

Sounds good! I updated it in my queue, and I will repost it in the
future pending test results and other comments.

thanks,

 - Joel