linux-kernel - Re: [PATCH V3] rxe: Fix a sleep-in-atomic bug in post_one

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Message-ID: <CAG9sBKMgUSdBEgub2V0VD4c9WLZYSfW+aU+dS887Pg_-1eucKA@mail.gmail.com>
Date:   Thu, 1 Jun 2017 12:32:29 +0300
From:   Moni Shoua <monis@...lanox.com>
To:     Jia-Ju Bai <baijiaju1990@....com>
Cc:     Sean Hefty <sean.hefty@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        Leon Romanovsky <leon@...nel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3] rxe: Fix a sleep-in-atomic bug in post_one_send

On Thu, Jun 1, 2017 at 11:28 AM, Jia-Ju Bai <baijiaju1990@....com> wrote:
> The driver may sleep under a spin lock, and the function call path is:
> post_one_send (acquire the lock by spin_lock_irqsave)
>   init_send_wqe
>     copy_from_user --> may sleep
>
> To fix it, the lock is released before copy_from_user, and the lock is
> acquired again after this function. The parameter "flags" is used to
> restore and save the irq status.
> Thank Leon for good advice.
>
> This patch corrects the mistakes in V2. (Thank Ram for pointing it out)
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
> ---
>  drivers/infiniband/sw/rxe/rxe_verbs.c |   13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
> index 83d709e..5293d15 100644
> --- a/drivers/infiniband/sw/rxe/rxe_verbs.c
> +++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
> @@ -721,11 +721,11 @@ static void init_send_wr(struct rxe_qp *qp, struct rxe_send_wr *wr,
>
>  static int init_send_wqe(struct rxe_qp *qp, struct ib_send_wr *ibwr,
>                          unsigned int mask, unsigned int length,
> -                        struct rxe_send_wqe *wqe)
> +                        struct rxe_send_wqe *wqe, unsigned long *flags)
>  {
>         int num_sge = ibwr->num_sge;
>         struct ib_sge *sge;
> -       int i;
> +       int i, err;
>         u8 *p;
>
>         init_send_wr(qp, &wqe->wr, ibwr);
> @@ -740,8 +740,11 @@ static int init_send_wqe(struct rxe_qp *qp, struct ib_send_wr *ibwr,
>
>                 sge = ibwr->sg_list;
>                 for (i = 0; i < num_sge; i++, sge++) {
> -                       if (qp->is_user && copy_from_user(p, (__user void *)
> -                                           (uintptr_t)sge->addr, sge->length))
> +                       spin_unlock_irqrestore(&qp->sq.sq_lock, *flags);

Before the patch, copy_from_user() was called only if qp->is_user was
true. After the patch it is always called.
Second, I think that  there is no flow that leads to this function
when qp->is user is true so maybe the correct action is to remove this
line completely

if (qp->is_user && copy_from_user(p, (__user void *)