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Message-ID: <20190528194342.GC20578@tower.DHCP.thefacebook.com> Date: Tue, 28 May 2019 19:43:46 +0000 From: Roman Gushchin <guro@...com> To: Stanislav Fomichev <sdf@...gle.com> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, "davem@...emloft.net" <davem@...emloft.net>, "ast@...nel.org" <ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net> Subject: Re: [PATCH bpf-next v3 3/4] bpf: cgroup: properly use bpf_prog_array api On Tue, May 28, 2019 at 11:29:45AM -0700, Stanislav Fomichev wrote: > Now that we don't have __rcu markers on the bpf_prog_array helpers, > let's use proper rcu_dereference_protected to obtain array pointer > under mutex. > > We also don't need __rcu annotations on cgroup_bpf.inactive since > it's not read/updated concurrently. > > v3: > * amend cgroup_rcu_dereference to include percpu_ref_is_dying; > cgroup_bpf is now reference counted and we don't hold cgroup_mutex > anymore in cgroup_bpf_release > > v2: > * replace xchg with rcu_swap_protected > > Cc: Roman Gushchin <guro@...com> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com> > --- > include/linux/bpf-cgroup.h | 2 +- > kernel/bpf/cgroup.c | 32 +++++++++++++++++++++----------- > 2 files changed, 22 insertions(+), 12 deletions(-) > > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h > index 9f100fc422c3..b631ee75762d 100644 > --- a/include/linux/bpf-cgroup.h > +++ b/include/linux/bpf-cgroup.h > @@ -72,7 +72,7 @@ struct cgroup_bpf { > u32 flags[MAX_BPF_ATTACH_TYPE]; > > /* temp storage for effective prog array used by prog_attach/detach */ > - struct bpf_prog_array __rcu *inactive; > + struct bpf_prog_array *inactive; > > /* reference counter used to detach bpf programs after cgroup removal */ > struct percpu_ref refcnt; > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > index d995edbe816d..118b70175dd9 100644 > --- a/kernel/bpf/cgroup.c > +++ b/kernel/bpf/cgroup.c > @@ -22,6 +22,13 @@ > DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key); > EXPORT_SYMBOL(cgroup_bpf_enabled_key); > > +#define cgroup_rcu_dereference(cgrp, p) \ > + rcu_dereference_protected(p, lockdep_is_held(&cgroup_mutex) || \ > + percpu_ref_is_dying(&cgrp->bpf.refcnt)) Some comments why percpu_ref_is_dying(&cgrp->bpf.refcnt) is enough here will be appreciated. Thanks!
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