[PATCH v4 -rcu 0/4] Maintain the length of each segment in the segcblist

[Joel Fernandes (Google)]

This is required for several usecases identified. One of them being tracing how
the segmented callback list changes. Tracing this has identified issues in RCU
code in the past. The trace patch is the last one in this series.

Passes 30 minutes of TREE01, TREE03, TREE07.  Testing of other TREE configs is
in progress.

Patches are based on -rcu commit:
4f43de2a419a ("Merge branch 'lkmm-dev.2020.08.24a' into HEAD")

Revision history:
v4: Restructured rcu_do_batch() and segcblist merging to avoid issues.
    Fixed minor nit from Davidlohr.
v1->v3: minor nits.
(https://lore.kernel.org/lkml/20200719034210.2382053-1-joel@xxxxxxxxxxxxxxxxx/)

Joel Fernandes (Google) (4):
rcu/segcblist: Do not depend on rcl->len to store the segcb len during
merge
rcu/tree: Make rcu_do_batch count how many callbacks were executed
rcu/segcblist: Add counters to segcblist datastructure
rcu/trace: Add tracing for how segcb list changes

include/linux/rcu_segcblist.h |   2 +
include/trace/events/rcu.h    |  25 +++++++
kernel/rcu/rcu_segcblist.c    | 119 ++++++++++++++++++++++++++++++++--
kernel/rcu/rcu_segcblist.h    |   8 +++
kernel/rcu/tree.c             |  32 +++++++--
5 files changed, 175 insertions(+), 11 deletions(-)

--
2.28.0.297.g1956fa8f8d-goog