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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@xxxxxxxxxx>
---
  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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