linux-kernel - Re: [PATCH v2] xsk: share the mmap

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Date:   Mon, 11 Feb 2019 17:21:49 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Bjorn Topel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Netdev <netdev@...r.kernel.org>, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH v2] xsk: share the mmap_sem for page pinning

Den mån 11 feb. 2019 kl 17:15 skrev Davidlohr Bueso <dave@...olabs.net>:
>
> Holding mmap_sem exclusively for a gup() is an overkill.
> Lets share the lock and replace the gup call for gup_longterm(),
> as it is better suited for the lifetime of the pinning.
>

Thanks for the cleanup!

Acked-by: Björn Töpel <bjorn.topel@...el.com>

> Cc: David S. Miller <davem@...emloft.net>
> Cc: Bjorn Topel <bjorn.topel@...el.com>
> Cc: Magnus Karlsson <magnus.karlsson@...el.com>
> CC: netdev@...r.kernel.org
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
>  net/xdp/xdp_umem.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index 5ab236c5c9a5..e7fa8d0d7090 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -265,10 +265,10 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem)
>         if (!umem->pgs)
>                 return -ENOMEM;
>
> -       down_write(&current->mm->mmap_sem);
> -       npgs = get_user_pages(umem->address, umem->npgs,
> +       down_read(&current->mm->mmap_sem);
> +       npgs = get_user_pages_longterm(umem->address, umem->npgs,
>                               gup_flags, &umem->pgs[0], NULL);
> -       up_write(&current->mm->mmap_sem);
> +       up_read(&current->mm->mmap_sem);
>
>         if (npgs != umem->npgs) {
>                 if (npgs >= 0) {
> --
> 2.16.4
>