Hello!
This is version 7 of a patch series creating a new notrace variant of
SRCU-fast for eventual use by the __DECLARE_TRACE() macro in place of the
current preemption disabling for PREEMPT_RT kernels. This change will
enable preemption of BPF programs attached to tracepoints in PREEMPT_RT
kernels, as is required for runtime use of BPF in real-time systems.
Non-PREEMPT_RT kernels will continue to have such BPF programs be
non-preemptible.
The patches are as follows:
1. Move rcu_is_watching() checks to srcu_read_{,un}lock_fast().
2. Add srcu_read_lock_fast_notrace() and
srcu_read_unlock_fast_notrace().
3. Add guards for notrace variants of SRCU-fast readers.
4. Document __srcu_read_{,un}lock_fast() implicit RCU readers.
5. Document srcu_flip() memory-barrier D relation to SRCU-fast.
6. Remove preempt_disable/enable() in srcu_gp_start_if_needed(),
courtesy of Zqiang.
Changes since v6:
o Deferred the application of SRCU-fast to __DECLARE_TRACE()
due to bugs located by the good services of kernel test robot.
Although the current version is looking good, it needs more
test time.
o Added patch 6.
Changes since v5:
o Forward-port to v6.17-rc1.
Changes since v4:
o Remove the redundant "notrace" tags per Boqun Feng feedback.
o Disable preemption for perf and ftrace per Steven Rostedt
feedback, which addresses the kernel test robot reports
provoked by earlier versions.
https://lore.kernel.org/all/45397494-544e-41c0-bf48-c66d213fce05@paulmck-laptop/
Changes since v3:
o Add "notrace" per Joel, Steven, and Matthew feedback.
o Upgrade explanatory comments and add new ones per Joel feedback.
https://lore.kernel.org/all/20250721162433.10454-1-paul...@kernel.org/
Changes since v2:
o Posting standalone as opposed to a reply.
https://lore.kernel.org/all/3cecf6c9-b2ee-4f34-9d1b-ca4cfb8e56a7@paulmck-laptop/
Changes since RFC version:
o RFC patch 6/4 has been pulled into the shared RCU tree:
e88c632a8698 ("srcu: Add guards for SRCU-fast readers")
o RFC patch 5/4 (which removed the now-unnecessary special boot-time
avoidance of SRCU) has been folded into patch 4/4 shown above,
as suggested by Steven Rostedt.
https://lore.kernel.org/all/bb20a575-235b-499e-aa1d-70fe9e2c7617@paulmck-laptop/
Thanx, Paul
------------------------------------------------------------------------
b/include/linux/srcu.h | 4 +++
b/include/linux/srcutree.h | 2 -
b/kernel/rcu/srcutiny.c | 4 ---
b/kernel/rcu/srcutree.c | 10 +++++++++
include/linux/srcu.h | 30 ++++++++++++++++++++++++++++
include/linux/srcutree.h | 47 ++++++++++++++++++++++++++++-----------------
6 files changed, 75 insertions(+), 22 deletions(-)
