| Message ID | 20210604063116.234316-5-memxor@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add bpf_link based TC-BPF API | expand |
On Fri, Jun 04, 2021 at 11:24:28PM IST, Alexei Starovoitov wrote: > On Fri, Jun 04, 2021 at 12:01:13PM +0530, Kumar Kartikeya Dwivedi wrote: > > This is used by BPF_LINK_UPDATE to replace the attach SCHED_CLS bpf prog > > effectively changing the classifier implementation for a given filter > > owned by a bpf_link. > > > > Note that READ_ONCE suffices in this case as the ordering for loads from > > the filter are implicitly provided by the data dependency on BPF prog > > pointer. > > > > On the writer side we can just use a relaxed WRITE_ONCE store to make > > sure one or the other value is visible to a reader in cls_bpf_classify. > > Lifetime is managed using RCU so bpf_prog_put path should wait until > > readers are done for old_prog. > > Should those be rcu_deref and rcu_assign_pointer ? > Typically the pointer would be __rcu annotated which would be > another small change in struct cls_bpf_prog. > That would make the life time easier to follow? > True, I'll make that change. > > All other parties accessing the BPF prog are under RTNL protection, so > > need no changes. > > > > Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>. > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > --- > > net/sched/cls_bpf.c | 55 +++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 53 insertions(+), 2 deletions(-) > > > > diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c > > index bf61ffbb7fd0..f23304685c48 100644 > > --- a/net/sched/cls_bpf.c > > +++ b/net/sched/cls_bpf.c > > @@ -9,6 +9,7 @@ > > * (C) 2013 Daniel Borkmann <dborkman@redhat.com> > > */ > > > > +#include <linux/atomic.h> > > #include <linux/module.h> > > #include <linux/types.h> > > #include <linux/skbuff.h> > > @@ -104,11 +105,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, > > /* It is safe to push/pull even if skb_shared() */ > > __skb_push(skb, skb->mac_len); > > bpf_compute_data_pointers(skb); > > - filter_res = BPF_PROG_RUN(prog->filter, skb); > > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > > __skb_pull(skb, skb->mac_len); > > } else { > > bpf_compute_data_pointers(skb); > > - filter_res = BPF_PROG_RUN(prog->filter, skb); > > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > > } > > > > if (prog->exts_integrated) { > > @@ -775,6 +776,55 @@ static int cls_bpf_link_detach(struct bpf_link *link) > > return 0; > > } > > > > +static int cls_bpf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, > > + struct bpf_prog *old_prog) > > +{ > > + struct cls_bpf_link *cls_link; > > + struct cls_bpf_prog cls_prog; > > + struct cls_bpf_prog *prog; > > + int ret; > > + > > + rtnl_lock(); > > + > > + cls_link = container_of(link, struct cls_bpf_link, link); > > + if (!cls_link->prog) { > > + ret = -ENOLINK; > > + goto out; > > + } > > + > > + prog = cls_link->prog; > > + > > + /* BPF_F_REPLACEing? */ > > + if (old_prog && prog->filter != old_prog) { > > + ret = -EINVAL; > > Other places like cgroup_bpf_replace and bpf_iter_link_replace > return -EPERM in such case. > Ok, will change. > > + goto out; > > + } > > + > > + old_prog = prog->filter; > > + > > + if (new_prog == old_prog) { > > + ret = 0; > > + goto out; > > + } > > + > > + cls_prog = *prog; > > + cls_prog.filter = new_prog; > > + > > + ret = cls_bpf_offload(prog->tp, &cls_prog, prog, NULL); > > + if (ret < 0) > > + goto out; > > + > > + WRITE_ONCE(prog->filter, new_prog); > > + > > + bpf_prog_inc(new_prog); > > + /* release our reference */ > > + bpf_prog_put(old_prog); > > + > > +out: > > + rtnl_unlock(); > > + return ret; > > +} > > + > > static void __bpf_fill_link_info(struct cls_bpf_link *link, > > struct bpf_link_info *info) > > { > > @@ -859,6 +909,7 @@ static const struct bpf_link_ops cls_bpf_link_ops = { > > .show_fdinfo = cls_bpf_link_show_fdinfo, > > #endif > > .fill_link_info = cls_bpf_link_fill_link_info, > > + .update_prog = cls_bpf_link_update, > > }; > > > > static inline char *cls_bpf_link_name(u32 prog_id, const char *name) > > -- > > 2.31.1 > > > > -- -- Kartikeya
On Thu, Jun 3, 2021 at 11:32 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > This is used by BPF_LINK_UPDATE to replace the attach SCHED_CLS bpf prog > effectively changing the classifier implementation for a given filter > owned by a bpf_link. > > Note that READ_ONCE suffices in this case as the ordering for loads from > the filter are implicitly provided by the data dependency on BPF prog > pointer. > > On the writer side we can just use a relaxed WRITE_ONCE store to make > sure one or the other value is visible to a reader in cls_bpf_classify. > Lifetime is managed using RCU so bpf_prog_put path should wait until > readers are done for old_prog. > > All other parties accessing the BPF prog are under RTNL protection, so > need no changes. > > Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>. > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > --- > net/sched/cls_bpf.c | 55 +++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 53 insertions(+), 2 deletions(-) > > diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c > index bf61ffbb7fd0..f23304685c48 100644 > --- a/net/sched/cls_bpf.c > +++ b/net/sched/cls_bpf.c > @@ -9,6 +9,7 @@ > * (C) 2013 Daniel Borkmann <dborkman@redhat.com> > */ > > +#include <linux/atomic.h> > #include <linux/module.h> > #include <linux/types.h> > #include <linux/skbuff.h> > @@ -104,11 +105,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, > /* It is safe to push/pull even if skb_shared() */ > __skb_push(skb, skb->mac_len); > bpf_compute_data_pointers(skb); > - filter_res = BPF_PROG_RUN(prog->filter, skb); > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > __skb_pull(skb, skb->mac_len); > } else { > bpf_compute_data_pointers(skb); > - filter_res = BPF_PROG_RUN(prog->filter, skb); > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > } > > if (prog->exts_integrated) { > @@ -775,6 +776,55 @@ static int cls_bpf_link_detach(struct bpf_link *link) > return 0; > } > > +static int cls_bpf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, > + struct bpf_prog *old_prog) > +{ > + struct cls_bpf_link *cls_link; > + struct cls_bpf_prog cls_prog; > + struct cls_bpf_prog *prog; > + int ret; > + > + rtnl_lock(); > + > + cls_link = container_of(link, struct cls_bpf_link, link); > + if (!cls_link->prog) { > + ret = -ENOLINK; > + goto out; > + } > + > + prog = cls_link->prog; > + > + /* BPF_F_REPLACEing? */ > + if (old_prog && prog->filter != old_prog) { > + ret = -EINVAL; > + goto out; > + } > + > + old_prog = prog->filter; > + > + if (new_prog == old_prog) { > + ret = 0; So the contract is that if update is successful, new_prog's refcount taken by link_update() in kernel/bpf/syscall.c is transferred here. On error, it will be bpf_prog_put() by link_update(). So here you don't need extra refcnt, but it's also not an error, so you need to bpf_prog_put(new_prog) explicitly to balance out refcnt. See how it's done for XDP, for example. > + goto out; > + } > + > + cls_prog = *prog; > + cls_prog.filter = new_prog; > + > + ret = cls_bpf_offload(prog->tp, &cls_prog, prog, NULL); > + if (ret < 0) > + goto out; > + > + WRITE_ONCE(prog->filter, new_prog); > + > + bpf_prog_inc(new_prog); and you don't need this, you already got the reference from link_update() > + /* release our reference */ > + bpf_prog_put(old_prog); > + > +out: > + rtnl_unlock(); > + return ret; > +} > + > static void __bpf_fill_link_info(struct cls_bpf_link *link, > struct bpf_link_info *info) > { > @@ -859,6 +909,7 @@ static const struct bpf_link_ops cls_bpf_link_ops = { > .show_fdinfo = cls_bpf_link_show_fdinfo, > #endif > .fill_link_info = cls_bpf_link_fill_link_info, > + .update_prog = cls_bpf_link_update, > }; > > static inline char *cls_bpf_link_name(u32 prog_id, const char *name) > -- > 2.31.1 >
On Tue, Jun 08, 2021 at 05:02:04AM IST, Andrii Nakryiko wrote: > On Thu, Jun 3, 2021 at 11:32 PM Kumar Kartikeya Dwivedi > <memxor@gmail.com> wrote: > > > > This is used by BPF_LINK_UPDATE to replace the attach SCHED_CLS bpf prog > > effectively changing the classifier implementation for a given filter > > owned by a bpf_link. > > > > Note that READ_ONCE suffices in this case as the ordering for loads from > > the filter are implicitly provided by the data dependency on BPF prog > > pointer. > > > > On the writer side we can just use a relaxed WRITE_ONCE store to make > > sure one or the other value is visible to a reader in cls_bpf_classify. > > Lifetime is managed using RCU so bpf_prog_put path should wait until > > readers are done for old_prog. > > > > All other parties accessing the BPF prog are under RTNL protection, so > > need no changes. > > > > Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>. > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > --- > > net/sched/cls_bpf.c | 55 +++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 53 insertions(+), 2 deletions(-) > > > > diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c > > index bf61ffbb7fd0..f23304685c48 100644 > > --- a/net/sched/cls_bpf.c > > +++ b/net/sched/cls_bpf.c > > @@ -9,6 +9,7 @@ > > * (C) 2013 Daniel Borkmann <dborkman@redhat.com> > > */ > > > > +#include <linux/atomic.h> > > #include <linux/module.h> > > #include <linux/types.h> > > #include <linux/skbuff.h> > > @@ -104,11 +105,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, > > /* It is safe to push/pull even if skb_shared() */ > > __skb_push(skb, skb->mac_len); > > bpf_compute_data_pointers(skb); > > - filter_res = BPF_PROG_RUN(prog->filter, skb); > > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > > __skb_pull(skb, skb->mac_len); > > } else { > > bpf_compute_data_pointers(skb); > > - filter_res = BPF_PROG_RUN(prog->filter, skb); > > + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); > > } > > > > if (prog->exts_integrated) { > > @@ -775,6 +776,55 @@ static int cls_bpf_link_detach(struct bpf_link *link) > > return 0; > > } > > > > +static int cls_bpf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, > > + struct bpf_prog *old_prog) > > +{ > > + struct cls_bpf_link *cls_link; > > + struct cls_bpf_prog cls_prog; > > + struct cls_bpf_prog *prog; > > + int ret; > > + > > + rtnl_lock(); > > + > > + cls_link = container_of(link, struct cls_bpf_link, link); > > + if (!cls_link->prog) { > > + ret = -ENOLINK; > > + goto out; > > + } > > + > > + prog = cls_link->prog; > > + > > + /* BPF_F_REPLACEing? */ > > + if (old_prog && prog->filter != old_prog) { > > + ret = -EINVAL; > > + goto out; > > + } > > + > > + old_prog = prog->filter; > > + > > + if (new_prog == old_prog) { > > + ret = 0; > > So the contract is that if update is successful, new_prog's refcount > taken by link_update() in kernel/bpf/syscall.c is transferred here. On > error, it will be bpf_prog_put() by link_update(). So here you don't > need extra refcnt, but it's also not an error, so you need to > bpf_prog_put(new_prog) explicitly to balance out refcnt. See how it's > done for XDP, for example. > Yes, thanks for spotting this. > > > + goto out; > > + } > > + > > + cls_prog = *prog; > > + cls_prog.filter = new_prog; > > + > > + ret = cls_bpf_offload(prog->tp, &cls_prog, prog, NULL); > > + if (ret < 0) > > + goto out; > > + > > + WRITE_ONCE(prog->filter, new_prog); > > + > > + bpf_prog_inc(new_prog); > > and you don't need this, you already got the reference from link_update() > So the reason I still keep an extra refcount is because the existing code on the netlink side assumes that. Even though the link itself holds a refcount for us, the actual freeing of cls_bpf_prog may happen independent of bpf_link. I'll add a comment for this. > > + /* release our reference */ > > + bpf_prog_put(old_prog); > > + > > +out: > > + rtnl_unlock(); > > + return ret; > > +} > > + > > static void __bpf_fill_link_info(struct cls_bpf_link *link, > > struct bpf_link_info *info) > > { > > @@ -859,6 +909,7 @@ static const struct bpf_link_ops cls_bpf_link_ops = { > > .show_fdinfo = cls_bpf_link_show_fdinfo, > > #endif > > .fill_link_info = cls_bpf_link_fill_link_info, > > + .update_prog = cls_bpf_link_update, > > }; > > > > static inline char *cls_bpf_link_name(u32 prog_id, const char *name) > > -- > > 2.31.1 > > -- Kartikeya
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c index bf61ffbb7fd0..f23304685c48 100644 --- a/net/sched/cls_bpf.c +++ b/net/sched/cls_bpf.c @@ -9,6 +9,7 @@ * (C) 2013 Daniel Borkmann <dborkman@redhat.com> */ +#include <linux/atomic.h> #include <linux/module.h> #include <linux/types.h> #include <linux/skbuff.h> @@ -104,11 +105,11 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, /* It is safe to push/pull even if skb_shared() */ __skb_push(skb, skb->mac_len); bpf_compute_data_pointers(skb); - filter_res = BPF_PROG_RUN(prog->filter, skb); + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); __skb_pull(skb, skb->mac_len); } else { bpf_compute_data_pointers(skb); - filter_res = BPF_PROG_RUN(prog->filter, skb); + filter_res = BPF_PROG_RUN(READ_ONCE(prog->filter), skb); } if (prog->exts_integrated) { @@ -775,6 +776,55 @@ static int cls_bpf_link_detach(struct bpf_link *link) return 0; } +static int cls_bpf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, + struct bpf_prog *old_prog) +{ + struct cls_bpf_link *cls_link; + struct cls_bpf_prog cls_prog; + struct cls_bpf_prog *prog; + int ret; + + rtnl_lock(); + + cls_link = container_of(link, struct cls_bpf_link, link); + if (!cls_link->prog) { + ret = -ENOLINK; + goto out; + } + + prog = cls_link->prog; + + /* BPF_F_REPLACEing? */ + if (old_prog && prog->filter != old_prog) { + ret = -EINVAL; + goto out; + } + + old_prog = prog->filter; + + if (new_prog == old_prog) { + ret = 0; + goto out; + } + + cls_prog = *prog; + cls_prog.filter = new_prog; + + ret = cls_bpf_offload(prog->tp, &cls_prog, prog, NULL); + if (ret < 0) + goto out; + + WRITE_ONCE(prog->filter, new_prog); + + bpf_prog_inc(new_prog); + /* release our reference */ + bpf_prog_put(old_prog); + +out: + rtnl_unlock(); + return ret; +} + static void __bpf_fill_link_info(struct cls_bpf_link *link, struct bpf_link_info *info) { @@ -859,6 +909,7 @@ static const struct bpf_link_ops cls_bpf_link_ops = { .show_fdinfo = cls_bpf_link_show_fdinfo, #endif .fill_link_info = cls_bpf_link_fill_link_info, + .update_prog = cls_bpf_link_update, }; static inline char *cls_bpf_link_name(u32 prog_id, const char *name)