On Wed, Jun 08, 2022 at 03:18:09PM -0300, Leonardo Bras wrote:
> Somewhere between v6 and v7 the of the zero-copy-send patchset a crucial
> part of the flushing mechanism got missing: incrementing zero_copy_queued.
>
> Without that, the flushing interface becomes a no-op, and there is no
> garantee the buffer is really sent.
>
> This can go as bad as causing a corruption in RAM during migration.
>
> Fixes: 2bc58ffc2926 ("QIOChannelSocket: Implement io_writev zero copy flag &
> io_flush for CONFIG_LINUX")
> Reported-by: 徐闯 <xuchuangxc...@bytedance.com>
> Signed-off-by: Leonardo Bras <leob...@redhat.com>
> ---
> io/channel-socket.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index dc9c165de1..ca4cae930f 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -554,6 +554,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
> size_t fdsize = sizeof(int) * nfds;
> struct cmsghdr *cmsg;
> int sflags = 0;
> + bool zero_copy_enabled = false;
>
> memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS));
>
> @@ -581,6 +582,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
> #ifdef QEMU_MSG_ZEROCOPY
> if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
> sflags = MSG_ZEROCOPY;
> + zero_copy_enabled = true;
> }
> #endif
>
> @@ -592,21 +594,24 @@ static ssize_t qio_channel_socket_writev(QIOChannel
> *ioc,
> return QIO_CHANNEL_ERR_BLOCK;
> case EINTR:
> goto retry;
> -#ifdef QEMU_MSG_ZEROCOPY
Removing this ifdef appears incidental to the change. If this is
redundant just remove it in its own patch.
> case ENOBUFS:
> - if (sflags & MSG_ZEROCOPY) {
> + if (zero_copy_enabled) {
> error_setg_errno(errp, errno,
> "Process can't lock enough memory for using
> MSG_ZEROCOPY");
> return -1;
> }
> break;
> -#endif
> }
>
> error_setg_errno(errp, errno,
> "Unable to write to socket");
> return -1;
> }
> +
> + if (zero_copy_enabled) {
What's wrong with
if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
sioc->zero_copy_queued++;
}
Introducing another local variable doesn't really add value IMHO.
With regards,
Daniel
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