MIME-Version: 1.0
References: <20230315181902.4177819-1-joel@joelfernandes.org>
 <20230315181902.4177819-13-joel@joelfernandes.org> <e704127e-1bfe-f351-db95-bfea6916e8f9@gmail.com>
 <CAEXW_YTB+LBG+oL02c0JfmAzoGSkZDM=QW1EXKbO3f-g0i4ddA@mail.gmail.com> <7a0dfc9f-6d21-fce4-4b83-72bb171454d3@gmail.com>
In-Reply-To: <7a0dfc9f-6d21-fce4-4b83-72bb171454d3@gmail.com>
From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Wed, 15 Mar 2023 15:59:54 -0400
Message-ID: <CAEXW_YTOC4KcnjP+oZEmUwhxT2RTRJUGZcK-bC2dZHNxQaWc5w@mail.gmail.com>
Subject: Re: [PATCH v2 13/14] RDMA/rxe: Rename kfree_rcu() to kvfree_rcu_mightsleep()
To:     Bob Pearson <rpearsonhpe@gmail.com>
Cc:     Zhu Yanjun <zyjzyj2000@gmail.com>, Jason Gunthorpe <jgg@ziepe.ca>,
        Leon Romanovsky <leon@kernel.org>,
        Devesh Sharma <devesh.s.sharma@oracle.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Zhu Yanjun <yanjun.zhu@linux.dev>, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Wed, Mar 15, 2023 at 3:05=E2=80=AFPM Bob Pearson <rpearsonhpe@gmail.com>=
 wrote:
>
> On 3/15/23 13:41, Joel Fernandes wrote:
> > On Wed, Mar 15, 2023 at 2:38=E2=80=AFPM Bob Pearson <rpearsonhpe@gmail.=
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 go=
al
> >>> 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@gmai=
l.com
> >>> Acked-by: Zhu Yanjun <zyjzyj2000@gmail.com>
> >>> Reviewed-by: Bob Pearson <rpearsonhpe@gmail.com>
> >>> Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> >>> Fixes: 72a03627443d ("RDMA/rxe: Remove rxe_alloc()")
> >>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.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_ud=
ata *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 clea=
nup code will disable
> looking up the mr from its rkey or lkey and then wait until all the refer=
ences to the mr are dropped
> before calling kfree. This will always work (unless a new bug is introduc=
ed) 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