From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Daniel Colascione <dancol@google.com>,
Joel Fernandes <joelaf@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Tim Murray <timmurray@google.com>,
netdev <netdev@vger.kernel.org>,
Lorenzo Colitti <lorenzo@google.com>,
Chenbo Feng <fengc@google.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
stable@vger.kernel.org
Subject: Re: [PATCH v4] Wait for running BPF programs when updating map-in-map
Date: Thu, 18 Oct 2018 08:46:59 -0700 [thread overview]
Message-ID: <20181018154657.ehgj3ozy62zy47hi@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAEXW_YQFs9mcw5Qv04ZRv=ZAK7YeBLJKByQxXYLj34iigS-Q=Q@mail.gmail.com>
On Tue, Oct 16, 2018 at 10:39:57AM -0700, Joel Fernandes wrote:
> On Fri, Oct 12, 2018 at 7:31 PM, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> > On Fri, Oct 12, 2018 at 03:54:27AM -0700, Daniel Colascione wrote:
> >> The map-in-map frequently serves as a mechanism for atomic
> >> snapshotting of state that a BPF program might record. The current
> >> implementation is dangerous to use in this way, however, since
> >> userspace has no way of knowing when all programs that might have
> >> retrieved the "old" value of the map may have completed.
> >>
> >> This change ensures that map update operations on map-in-map map types
> >> always wait for all references to the old map to drop before returning
> >> to userspace.
> >>
> >> Signed-off-by: Daniel Colascione <dancol@google.com>
> >> ---
> >> kernel/bpf/syscall.c | 14 ++++++++++++++
> >> 1 file changed, 14 insertions(+)
> >>
> >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> >> index 8339d81cba1d..d7c16ae1e85a 100644
> >> --- a/kernel/bpf/syscall.c
> >> +++ b/kernel/bpf/syscall.c
> >> @@ -741,6 +741,18 @@ static int map_lookup_elem(union bpf_attr *attr)
> >> return err;
> >> }
> >>
> >> +static void maybe_wait_bpf_programs(struct bpf_map *map)
> >> +{
> >> + /* Wait for any running BPF programs to complete so that
> >> + * userspace, when we return to it, knows that all programs
> >> + * that could be running use the new map value.
> >> + */
> >> + if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS ||
> >> + map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS) {
> >> + synchronize_rcu();
> >> + }
> >
> > extra {} were not necessary. I removed them while applying to bpf-next.
> > Please run checkpatch.pl next time.
> > Thanks
>
> Thanks Alexei for taking it. Me and Lorenzo were discussing that not
> having this causes incorrect behavior for apps using map-in-map for
> this. So I CC'd stable as well.
It is too late in the release cycle.
We can submit it to stable releases after the merge window.
next prev parent reply other threads:[~2018-10-18 15:47 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAKOZuesQ6GdNTGDFsNi4o8LYzxLBtYZ=Cz4=aZbqqCNia+QFnQ@mail.gmail.com>
2018-07-29 20:58 ` [PATCH v3] Add BPF_SYNCHRONIZE_MAP_TO_MAP_REFERENCES bpf(2) command Daniel Colascione
2018-07-30 10:04 ` Daniel Borkmann
2018-07-30 10:25 ` Daniel Colascione
2018-07-31 0:26 ` Jakub Kicinski
2018-07-31 0:33 ` Daniel Colascione
2018-07-31 0:45 ` Jakub Kicinski
2018-07-31 0:50 ` Daniel Colascione
2018-07-31 1:14 ` Jakub Kicinski
2018-07-31 8:34 ` Daniel Borkmann
2018-07-31 9:36 ` Daniel Colascione
2018-08-10 22:52 ` Alexei Starovoitov
2018-08-14 20:37 ` Daniel Colascione
2018-08-16 4:01 ` Alexei Starovoitov
2018-10-12 10:54 ` [PATCH v4] Wait for running BPF programs when updating map-in-map Daniel Colascione
2018-10-12 20:54 ` Joel Fernandes
2018-10-13 2:31 ` Alexei Starovoitov
2018-10-16 17:39 ` Joel Fernandes
2018-10-18 15:46 ` Alexei Starovoitov [this message]
2018-10-18 23:36 ` Joel Fernandes
2018-11-10 2:01 ` Chenbo Feng
2018-11-10 15:22 ` Greg KH
2018-11-10 18:58 ` Chenbo Feng
[not found] ` <CAKOZues6SE_c=ix7ap6QaJHqd1TmYpWWMJiu3=TtuqgKuqOUCA@mail.gmail.com>
2018-08-10 22:29 ` [PATCH v3] Add BPF_SYNCHRONIZE_MAP_TO_MAP_REFERENCES bpf(2) command Alexei Starovoitov
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