From: Daniel Colascione <dancol@google.com>
To: joelaf@google.com
Cc: linux-kernel@vger.kernel.org, timmurray@google.com,
netdev@vger.kernel.org,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
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>,
Daniel Colascione <dancol@google.com>
Subject: [PATCH v4] Wait for running BPF programs when updating map-in-map
Date: Fri, 12 Oct 2018 03:54:27 -0700 [thread overview]
Message-ID: <20181012105427.243779-1-dancol@google.com> (raw)
In-Reply-To: <20180816040145.gqzqicab4s6kcbye@ast-mbp.dhcp.thefacebook.com>
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();
+ }
+}
+
#define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags
static int map_update_elem(union bpf_attr *attr)
@@ -831,6 +843,7 @@ static int map_update_elem(union bpf_attr *attr)
}
__this_cpu_dec(bpf_prog_active);
preempt_enable();
+ maybe_wait_bpf_programs(map);
out:
free_value:
kfree(value);
@@ -883,6 +896,7 @@ static int map_delete_elem(union bpf_attr *attr)
rcu_read_unlock();
__this_cpu_dec(bpf_prog_active);
preempt_enable();
+ maybe_wait_bpf_programs(map);
out:
kfree(key);
err_put:
--
2.19.0.605.g01d371f741-goog
next prev parent reply other threads:[~2018-10-12 10:54 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 ` Daniel Colascione [this message]
2018-10-12 20:54 ` [PATCH v4] Wait for running BPF programs when updating map-in-map Joel Fernandes
2018-10-13 2:31 ` Alexei Starovoitov
2018-10-16 17:39 ` Joel Fernandes
2018-10-18 15:46 ` Alexei Starovoitov
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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