Messages in this thread Patch in this message | | | Date | Fri, 6 Jul 2018 18:56:16 -0700 | Subject | [RFC] Add BPF_SYNCHRONIZE bpf(2) command | From | Daniel Colascione <> |
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BPF_SYNCHRONIZE waits for any BPF programs active at the time of BPF_SYNCHRONIZE to complete, allowing userspace to ensure atomicity of RCU data structure operations with respect to active programs. For example, userspace can update a map->map entry to point to a new map, use BPF_SYNCHRONIZE to wait for any BPF programs using the old map to complete, and then drain the old map without fear that BPF programs may still be updating it.
Signed-off-by: Daniel Colascione <dancol@google.com> --- include/uapi/linux/bpf.h | 1 + kernel/bpf/syscall.c | 14 ++++++++++++++ 2 files changed, 15 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index b7db3261c62d..4365c50e8055 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -98,6 +98,7 @@ enum bpf_cmd { BPF_BTF_LOAD, BPF_BTF_GET_FD_BY_ID, BPF_TASK_FD_QUERY, + BPF_SYNCHRONIZE, }; enum bpf_map_type { diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index d10ecd78105f..60ec7811846e 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2272,6 +2272,20 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN)) return -EPERM; + if (cmd == BPF_SYNCHRONIZE) { + if (uattr != NULL || size != 0) + return -EINVAL; + err = security_bpf(cmd, NULL, 0); + if (err < 0) + return err; + /* BPF programs are run with preempt disabled, so + * synchronize_sched is sufficient even with + * RCU_PREEMPT. + */ + synchronize_sched(); + return 0; + } + err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size); if (err) return err; -- 2.18.0.203.gfac676dfb9-goog
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