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Date: Tue, 3 Mar 2020 10:11:59 +0000
From: Julien Grall <julien@....org>
To: Dongli Zhang <dongli.zhang@...cle.com>,
xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc: jgross@...e.com, boris.ostrovsky@...cle.com,
sstabellini@...nel.org, joe.jin@...cle.com
Subject: Re: [Xen-devel] [PATCH 2/2] xenbus: req->err should be updated before
req->state
Hi,
On 03/03/2020 01:58, Dongli Zhang wrote:
> This patch adds the barrier to guarantee that req->err is always updated
> before req->state.
>
> Otherwise, read_reply() would not return ERR_PTR(req->err) but
> req->body, when process_writes()->xb_write() is failed.
The memory barrier below looks good. However, as mentionned in patch #1,
barrier() is not the correct barrier to pair with virt_wmb().
>
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
> drivers/xen/xenbus/xenbus_comms.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
> index 852ed161fc2a..eb5151fc8efa 100644
> --- a/drivers/xen/xenbus/xenbus_comms.c
> +++ b/drivers/xen/xenbus/xenbus_comms.c
> @@ -397,6 +397,8 @@ static int process_writes(void)
> if (state.req->state == xb_req_state_aborted)
> kfree(state.req);
> else {
> + /* write err, then update state */
> + virt_wmb();
> state.req->state = xb_req_state_got_reply;
> wake_up(&state.req->wq);
> }
>
Cheers,
--
Julien Grall
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