RE: [PATCH] Retry infinitely for hypercall

Long Li
2017-01-04T22:07:22Z

> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@oracle.com]
> Sent: Wednesday, January 4, 2017 1:48 PM
> To: Long Li <longli@microsoft.com>
> Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; devel@linuxdriverproject.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH] Retry infinitely for hypercall
>
> Fix the subsystem prefix in the subject.
>
> On Wed, Jan 04, 2017 at 02:39:31PM -0800, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > Hyper-v host guarantees that a hypercall will succeed. Retry infinitely to
> avoid returning transient failures to upper layer.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> > drivers/hv/connection.c | 17 ++++++++---------
> > 1 file changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c index
> > 6ce8b87..4bcb099 100644
> > --- a/drivers/hv/connection.c
> > +++ b/drivers/hv/connection.c
> > @@ -439,7 +439,6 @@ int vmbus_post_msg(void *buffer, size_t buflen) {
> > union hv_connection_id conn_id;
> > int ret = 0;
>
> Btw, when you disable GCC's uninitialized variable checking by storing bogus
> values in "ret", it's eventually going to bite you in the bum.
> Eventually you're going to get a bug that should have been detected through
> static analysis if only you hadn't disabled it.
>
> > - int retries = 0;
> > u32 usec = 1;
> >
> > conn_id.asu32 = 0;
> > @@ -447,10 +446,10 @@ int vmbus_post_msg(void *buffer, size_t buflen)
> >
> > /*
> > * hv_post_message() can have transient failures because of
> > - * insufficient resources. Retry the operation a couple of
> > - * times before giving up.
> > + * insufficient resources. We retry infinitely on these failures
> > + * because host guarantees hypercall will eventually succeed.
> > */
> > - while (retries < 20) {
> > + while (1) {
> > ret = hv_post_message(conn_id, 1, buffer, buflen);
> >
> > switch (ret) {
> > @@ -459,11 +458,11 @@ int vmbus_post_msg(void *buffer, size_t buflen)
> > * We could get this if we send messages too
> > * frequently.
> > */
>
> Move the comment above the code it's commenting about.
>
> /*
> * We could get INVALID_CONNECTION_ID if we flood the
> * host with too many messages.
> */
> case HV_STATUS_INVALID_CONNECTION_ID:
> case HV_STATUS_INSUFFICIENT_MEMORY:
> case HV_STATUS_INSUFFICIENT_BUFFERS:
> break;
>
>
>
> > - ret = -EAGAIN;
> > - break;
> > case HV_STATUS_INSUFFICIENT_MEMORY:
> > case HV_STATUS_INSUFFICIENT_BUFFERS:
> > - ret = -ENOMEM;
> > + /*
> > + * Temporary failure out of resources
> > + */
> > break;
> > case HV_STATUS_SUCCESS:
> > return ret;
>
> return 0;
>
> Better to be more explicit. When I looked at this I got briefly confused if this
> function was supposed to return HV_ statuses or standard kernel error
> codes. It turns out that HV_STATUS_SUCCESS is zero the success returns
> map directly to linux kernel code for success but it's clearer to be explicit.
>
> > @@ -472,12 +471,12 @@ int vmbus_post_msg(void *buffer, size_t buflen)
> > return -EINVAL;
> > }
>
> > - retries++;
> > udelay(usec);
> > if (usec < 2048)
> > usec *= 2;
> > }
> > - return ret;
> > + /* Impossible to get here */
> > + BUG_ON(1);
>
> Remove the comment and the BUG_ON().
>
> regards,
> dan carpenter

Thanks, I will fix those in V2.

Long