On 4 May 2023, at 13:29, Peng He wrote:
> The following comments (brought in at 0de8783a9):
>
> /* XXX: There's a race window where a flow covering this packet
> * could have already been installed since we last did the flow
> * lookup before upcall. This could be solved by moving the
> * mutex lock outside the loop, but that's an awful long time
> * to be locking revalidators out of making flow modifications. */
>
> is out-dated. Back at commit 0de8783a9, the classifier is per-datapath,
> multiple PMDs share a same classifier. Since now we have changed into
> per-PMD classifier, the lookup code only prevents from the race
> results from megaflows installed by another non-pmd threads, through
> either manually calling dpctl/add-flow or handler thread installing
> megaflow with pmd-id == PMD_ID_NULL, there are no other threads which
> would insert datapath flows.
Thanks this looks good to me. Will try to review patch 1/2 next week.
Acked-by: Eelco Chaudron <[email protected]>
> Signed-off-by: Peng He <[email protected]>
> ---
> lib/dpif-netdev.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 70b953ae6..d92ec01fb 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -8403,12 +8403,11 @@ handle_packet_upcall(struct dp_netdev_pmd_thread *pmd,
> if (OVS_LIKELY(error != ENOSPC)) {
> struct dp_netdev_flow *netdev_flow;
>
> - /* XXX: There's a race window where a flow covering this packet
> - * could have already been installed since we last did the flow
> - * lookup before upcall. This could be solved by moving the
> - * mutex lock outside the loop, but that's an awful long time
> - * to be locking revalidators out of making flow modifications. */
> ovs_mutex_lock(&pmd->flow_mutex);
> + /* Two scenarios exist where a flow could have been added while
> + * processing the upcall:
> + * 1) a flow was manually added through dpctl/add-flow.
> + * 2) a handler installed a flow with pmd-id == PMD_ID_NULL. */
> netdev_flow = dp_netdev_pmd_lookup_flow(pmd, key, NULL);
> if (OVS_LIKELY(!netdev_flow)) {
> netdev_flow = dp_netdev_flow_add(pmd, &match, &ufid,
> --
> 2.25.1
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