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Re: [PATCH v2] SUNRPC: Fix TCP receive code on archs with flush_dcache_p

To: Trond Myklebust <trondmy@gmail.com>
Subject: Re: [PATCH v2] SUNRPC: Fix TCP receive code on archs with flush_dcache_page()
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 3 Jan 2019 11:16:29 +0100
Cc: "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>, Linux MIPS Mailing List <linux-mips@linux-mips.org>
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Hi Trond,

On Thu, Jan 3, 2019 at 7:14 AM Trond Myklebust <trondmy@gmail.com> wrote:
> After receiving data into the page cache, we need to call flush_dcache_page()
> for the architectures that define it.
>
> Fixes: 277e4ab7d530b ("SUNRPC: Simplify TCP receive code by switching...")
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> Cc: stable@vger.kernel.org # v4.20

Thanks for your patch!

> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -48,6 +48,7 @@
>  #include <net/udp.h>
>  #include <net/tcp.h>
>  #include <linux/bvec.h>
> +#include <linux/highmem.h>
>  #include <linux/uio.h>
>
>  #include <trace/events/sunrpc.h>
> @@ -380,6 +381,27 @@ xs_read_discard(struct socket *sock, struct msghdr *msg, 
> int flags,
>         return sock_recvmsg(sock, msg, flags);
>  }
>
> +#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
> +static void
> +xs_flush_bvec(const struct bio_vec *bvec, size_t count, size_t seek)
> +{
> +       struct bvec_iter bi, __start = {

As for_each_bvec() assigns __start to bi, and you don't need __start
afterwards, both variables can be merged into a single one.
But perhaps that would make too many assumptions about the
implementation of for_each_bvec()?

> +               .bi_size = count,
> +       };
> +       struct bio_vec bv;
> +
> +       bvec_iter_advance(bvec, &__start, seek & PAGE_MASK);
> +
> +       for_each_bvec(bv, bvec, bi, __start)
> +               flush_dcache_page(bv.bv_page);
> +}
> +#else
> +static inline void
> +xs_flush_bvec(const struct bio_vec *bvec, size_t count, size_t seek)
> +{
> +}
> +#endif
> +
>  static ssize_t
>  xs_read_xdr_buf(struct socket *sock, struct msghdr *msg, int flags,
>                 struct xdr_buf *buf, size_t count, size_t seek, size_t *read)
> @@ -413,6 +435,7 @@ xs_read_xdr_buf(struct socket *sock, struct msghdr *msg, 
> int flags,
>                                 seek + buf->page_base);
>                 if (ret <= 0)
>                         goto sock_err;
> +               xs_flush_bvec(buf->bvec, ret, seek + buf->page_base);
>                 offset += ret - buf->page_base;
>                 if (offset == count || msg->msg_flags & (MSG_EOR|MSG_TRUNC))
>                         goto out;

I don't understand the code well enough to see why the call to
xs_flush_bvec() is needed in this branch only, but it does fix TCP
NFS on RBTX4927, so
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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