Re: [PATCH] vdpa/sfc: resolve race between libvhost and dev_conf

[David Marchand <david.marchand@redhat.com>]

Hello Abhimanyu, Vijay,

On Thu, Jul 7, 2022 at 2:38 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
> On 7/6/22 11:24, abhimanyu.saini@xilinx.com wrote:
> > From: Abhimanyu Saini <absaini@amd.com>
> >
> > libvhost calls dev_conf() before prosessing the
> > VHOST_USER_SET_VRING_CALL message for the last VQ. So
> > this message is processed after dev_conf() returns.
> >
> > However, the dev_conf() function spawns a thread to set
> > rte_vhost_host_notifier_ctrl() before returning control to
> > libvhost. This parallel thread in turn invokes get_notify_area().
> > To get the notify_area, the vdpa driver needs to query the HW and
> > for this query it needs an enabled VQ.
> >
> > But at the same time libvhost is processing the last
> > VHOST_USER_SET_VRING_CALL, and to do that it disables the last VQ.
> >
> > Hence there is a race b/w the libvhost and the vdpa driver.
> >
> > To resolve this race condition, query the HW and cache notify_area
> > inside dev_conf() instead of doing it the parallel thread.
> >
> > Signed-off-by: Abhimanyu Saini <absaini@amd.com>
> > ---
> >   drivers/vdpa/sfc/sfc_vdpa_ops.c | 36 ++++++++++++++++++------------------
> >   drivers/vdpa/sfc/sfc_vdpa_ops.h |  1 +
> >   2 files changed, 19 insertions(+), 18 deletions(-)
> >
>
> During today's Release status meeting, Andrew mentioned that this patch
> has been for a log time already in your internal tree.
>
> So it gives a bit of confidence in taking it in -rc4.

- But it is neither reviewed, nor acked by the driver maintainer.

Vijay, as this driver maintainer, your opinion matters.
We are in rc4 stage and we merge only critical fixes now.
There won't be much time to test this fix once merged (and I am not
talking about fixing a regression).

Are you confident with this fix? is it required for the 22.07 release?

If we don't get an answer, the safer is to let those fixes slip to a
next release.


- Besides, I see there is a new fix for some sfc driver.
https://patches.dpdk.org/project/dpdk/patch/20220708073702.29391-1-asaini@xilinx.com/
The same questions will be asked.


-- 
David Marchand