On Thu, Nov 30, 2023 at 10:01:18PM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> When removing the inner map from the outer map, the inner map will be
> freed after one RCU grace period and one RCU tasks trace grace
> period, so it is certain that the bpf program, which may access the
> inner map, has exited before the inner map is freed.
>
> However there is no need to wait for one RCU tasks trace grace period if
> the outer map is only accessed by non-sleepable program. So adding
> sleepable_refcnt in bpf_map and increasing sleepable_refcnt when adding
> the outer map into env->used_maps for sleepable program. Considering the
> max number of bpf program is INT_MAX - 1, atomic_t instead of atomic64_t
> is used for sleepable_refcnt. When removing the inner map from the outer
> map, using sleepable_refcnt to decide whether or not a RCU tasks trace
> grace period is needed before freeing the inner map.
Optimizing too soon as usual?
I bet you saw that we use:
atomic64_t refcnt
for bpf_map, but you probably didn't dig into git history and
missed commit 92117d8443bc ("bpf: fix refcnt overflow") ?
