On 11/3/22 3:29 PM, Kumar Kartikeya Dwivedi wrote:
On Fri, Nov 04, 2022 at 02:30:55AM IST, Yonghong Song wrote:
On 11/3/22 7:28 AM, KP Singh wrote:
On Thu, Nov 3, 2022 at 8:21 AM Yonghong Song <yhs@xxxxxx> wrote:
Add bpf_rcu_read_lock() and bpf_rcu_read_unlock() helpers.
Both helpers are available to all program types with
CAP_BPF capability.
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
include/linux/bpf.h | 2 ++
include/uapi/linux/bpf.h | 14 ++++++++++++++
kernel/bpf/core.c | 2 ++
kernel/bpf/helpers.c | 26 ++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 14 ++++++++++++++
5 files changed, 58 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8d948bfcb984..a9bda4c91fc7 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2554,6 +2554,8 @@ extern const struct bpf_func_proto bpf_get_retval_proto;
extern const struct bpf_func_proto bpf_user_ringbuf_drain_proto;
extern const struct bpf_func_proto bpf_cgrp_storage_get_proto;
extern const struct bpf_func_proto bpf_cgrp_storage_delete_proto;
+extern const struct bpf_func_proto bpf_rcu_read_lock_proto;
+extern const struct bpf_func_proto bpf_rcu_read_unlock_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 94659f6b3395..e86389cd6133 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5481,6 +5481,18 @@ union bpf_attr {
* 0 on success.
*
* **-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * void bpf_rcu_read_lock(void)
+ * Description
+ * Call kernel rcu_read_lock().
Simple wrapper around rcu_read_lock() and maybe explain where and how
it is supposed to
be used.
e.g. the verifier will check if __rcu pointers are being accessed with
bpf_rcu_read_lock in
sleepable programs.
Okay, I can add more descriptions.
Calling the helper from a non-sleepable program is inconsequential,
but maybe we can even
avoid exposing it to non-sleepable programs?
I actually debated myself whether to make bpf_rcu_read_lock()/unlock()
to be sleepable only. Although it won't hurt for non-sleepable program,
I guess I can make it as sleepable only so users don't make mistake
to use them in non-sleepable programs.
It's better to let it be a noop in non-sleepable programs but still allow
calling it. It allows writing common helper functions in the BPF program that
work in both sleepable and non-sleepable cases by holding the RCU read lock.
yes, I can do it. The verifier can rewrite it to a nop for non-sleepable
program to minimize runtime overhead.
