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| author | Toke Høiland-Jørgensen <toke@redhat.com> | 2021-06-24 19:05:53 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-06-24 20:41:14 +0300 |
| commit | e74c74f9e51deb725e72d129084ba8252d47222d (patch) | |
| tree | 7d52ec628c6aa39a9123dd851a85479298bca25d /Documentation/RCU/checklist.rst | |
| parent | 9a145c04a293933002ec288a4d6b4f370b59e4d1 (diff) | |
| download | linux-e74c74f9e51deb725e72d129084ba8252d47222d.tar.xz | |
doc: Give XDP as example of non-obvious RCU reader/updater pairing
This commit gives an example of non-obvious RCU reader/updater pairing
in the guise of the XDP feature in networking, which calls BPF programs
from network-driver NAPI (softirq) context.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210624160609.292325-4-toke@redhat.com
Diffstat (limited to 'Documentation/RCU/checklist.rst')
| -rw-r--r-- | Documentation/RCU/checklist.rst | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index 07f6cb8f674d..01cc21f17f7b 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -236,8 +236,15 @@ over a rather long period of time, but improvements are always welcome! Mixing things up will result in confusion and broken kernels, and has even resulted in an exploitable security issue. Therefore, - when using non-obvious pairs of primitives, commenting is of - course a must. + when using non-obvious pairs of primitives, commenting is + of course a must. One example of non-obvious pairing is + the XDP feature in networking, which calls BPF programs from + network-driver NAPI (softirq) context. BPF relies heavily on RCU + protection for its data structures, but because the BPF program + invocation happens entirely within a single local_bh_disable() + section in a NAPI poll cycle, this usage is safe. The reason + that this usage is safe is that readers can use anything that + disables BH when updaters use call_rcu() or synchronize_rcu(). 8. Although synchronize_rcu() is slower than is call_rcu(), it usually results in simpler code. So, unless update performance is |