Hou Tao <houtao@xxxxxxxxxxxxxxx> writes:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> After synchronize_rcu(), both the dettached XDP program and
> xdp_do_flush() are completed, and the only user of bpf_cpu_map_entry
> will be cpu_map_kthread_run(), so instead of calling
> __cpu_map_entry_replace() to empty queue and do cleanup after a RCU
> grace period, do these things directly.
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
With one nit below:
Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
> kernel/bpf/cpumap.c | 17 ++++++++---------
> 1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 24f39c37526f..f8e2b24320c0 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -554,16 +554,15 @@ static void cpu_map_free(struct bpf_map *map)
> /* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
> * so the bpf programs (can be more than one that used this map) were
> * disconnected from events. Wait for outstanding critical sections in
> - * these programs to complete. The rcu critical section only guarantees
> - * no further "XDP/bpf-side" reads against bpf_cpu_map->cpu_map.
> - * It does __not__ ensure pending flush operations (if any) are
> - * complete.
> + * these programs to complete. synchronize_rcu() below not only
> + * guarantees no further "XDP/bpf-side" reads against
> + * bpf_cpu_map->cpu_map, but also ensure pending flush operations
> + * (if any) are complete.
> */
> -
> synchronize_rcu();
>
> - /* For cpu_map the remote CPUs can still be using the entries
> - * (struct bpf_cpu_map_entry).
> + /* The only possible user of bpf_cpu_map_entry is
> + * cpu_map_kthread_run().
> */
> for (i = 0; i < cmap->map.max_entries; i++) {
> struct bpf_cpu_map_entry *rcpu;
> @@ -572,8 +571,8 @@ static void cpu_map_free(struct bpf_map *map)
> if (!rcpu)
> continue;
>
> - /* bq flush and cleanup happens after RCU grace-period */
> - __cpu_map_entry_replace(cmap, i, NULL); /* call_rcu */
> + /* Empty queue and do cleanup directly */
The "empty queue" here is a bit ambiguous, maybe "Stop kthread and
cleanup entry"?
> + __cpu_map_entry_free(&rcpu->free_work.work);
> }
> bpf_map_area_free(cmap->cpu_map);
> bpf_map_area_free(cmap);
> --
> 2.29.2
