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

["Saini, Abhimanyu" <abhimanyu.saini@amd.com>]

[AMD Official Use Only - General]

Sorry Maxime, I forgot to copy stable.
Yes it's required, the faulty commit is : 630be406dcbfc26260e9d9688c40a381d0f012db

-----Original Message-----
From: Maxime Coquelin <maxime.coquelin@redhat.com> 
Sent: Friday, July 8, 2022 2:55 PM
To: abhimanyu.saini@xilinx.com; dev@dpdk.org
Cc: chenbo.xia@intel.com; andrew.rybchenko@oktetlabs.ru; Saini, Abhimanyu <abhimanyu.saini@amd.com>
Subject: Re: [PATCH] vdpa/sfc: resolve race between libvhost and dev_conf

[CAUTION: External Email]

On 7/8/22 11:23, Maxime Coquelin 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(-)
>>
>
> Applied to dpdk-next-virtio/main.

Sorry, I notice it is missing the Fixes tag, and cc'ing stable.
Can you confirm this is needed and provide the faulty commit?

Thanks,
Maxime

> Thanks,
> Maxime