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Message-ID: <20251201120524.15568-1-frederic@kernel.org>
Date: Mon, 1 Dec 2025 13:05:24 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <frederic@...nel.org>,
"Paul E . McKenney" <paulmck@...nel.org>,
Joel Fernandes <joelagnelf@...dia.com>,
Neeraj Upadhyay <neeraj.upadhyay@....com>,
Uladzislau Rezki <urezki@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
rcu <rcu@...r.kernel.org>
Subject: [GIT PULL] RCU updates for v6.19
Hi Linus,
The following changes since commit 3a8660878839faadb4f1a6dd72c3179c1df56787:
Linux 6.18-rc1 (2025-10-12 13:42:36 -0700)
are available in the Git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git tags/rcu.release.v6.19
for you to fetch changes up to 9a08942f17017b708991c5089843d4a1bfac4420:
Merge branch 'rcu/misc' into next (2025-11-30 22:20:33 +0100)
----------------------------------------------------------------
RCU pull request for v6.19
SRCU
----
_ Properly handle SRCU readers within IRQ disabled sections in tiny SRCU
- Preparation to reimplement RCU Tasks Trace on top of SRCU fast:
- Introduce API to expedite a grace period and test it through
rcutorture.
- Split srcu-fast in two flavours: SRCU-fast and SRCU-fast-updown.
Both are still targeted toward faster readers (without full
barriers on LOCK and UNLOCK) at the expense of heavier write side
(using full RCU grace period ordering instead of simply full
ordering) as compared to "traditional" non-fast SRCU. But those
srcu-fast flavours are going to be optimized in two different
ways:
- SRCU-fast will become the reimplementation basis for
RCU-TASK-TRACE for consolidation. Since RCU-TASK-TRACE must
be NMI safe, SRCU-fast must be as well.
- SRCU-fast-updown will be needed for uretprobes code in order
to get rid of the read-side memory barriers while still
allowing entering the reader at task level while exiting it
in a timer handler. It is considered semaphore-like in that
it can have different owners between LOCK and UNLOCK.
However it is not NMI-safe.
The actual optimizations are work in progress for the next cycle.
Only the new interfaces are added for now, along with related
torture and scalability test code.
- Create/document/debug/torture new proper initializers for RCU fast:
DEFINE_SRCU_FAST() and init_srcu_struct_fast()
This allows for using right away the proper ordering on the write
side (either full ordering or full RCU grace period ordering) without
waiting for the read side to tell which to use. Also this optimizes
the read side altogether with moving flavour debug checks under debug
config and with removing a costly RmW operation on their first call.
- Make some diagnostic functions tracing safe.
REFSCALE
-------
Add performance testing for common context synchronizations
(Preemption, IRQ, Softirq) and per-cpu increments. Those are
relevant comparisons against SRCU-fast read side APIs, especially
as they are planned to synchronize further tracing fast-path code.
MISCELLANOUS
------
- In order to prepare the layout for nohz_full work deferral to
user exit, the context tracking state must shrink the counter
of transitions to/from RCU not watching. The only possible hazard
is to trigger wrap-around more easily, delaying a bit grace periods
when that happens. This should be a rare event though. Yet add
debugging and torture code to test that assumption.
- Fix memory leak on locktorture module
- Annotate accesses in rculist_nulls.h to prevent from KCSAN warnings.
On recent discussions, we also concluded that all those WRITE_ONCE()
and READ_ONCE() on list APIs deserve appropriate comments. Something
to be expected for the next cycle.
- Provide a script to apply several configs to several commits with torture.
- Allow torture to reuse a build directory in order to save needless
rebuild time.
- Various cleanups.
No known conflicts.
----------------------------------------------------------------
Frederic Weisbecker (3):
Merge branch 'rcu/srcu' into next
Merge branch 'rcu/refscale' into next
Merge branch 'rcu/misc' into next
Paul E. McKenney (25):
srcu: Permit Tiny SRCU srcu_read_unlock() with interrupts disabled
srcu: Create an srcu_expedite_current() function
rcutorture: Test srcu_expedite_current()
srcu: Create a DEFINE_SRCU_FAST()
srcu: Make grace-period determination use ssp->srcu_reader_flavor
rcutorture: Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast()
srcu: Require special srcu_struct define/init for SRCU-fast readers
srcu: Make SRCU-fast readers enforce use of SRCU-fast definition/init
doc: Update for SRCU-fast definitions and initialization
torture: Add kvm-series.sh to test commit/scenario combination
rcutorture: Permit kvm-again.sh to re-use the build directory
rcutorture: Remove redundant rcutorture_one_extend() from rcu_torture_one_read()
rcu: Mark diagnostic functions as notrace
srcu: Add SRCU_READ_FLAVOR_FAST_UPDOWN CPP macro
torture: Permit negative kvm.sh --kconfig numberic arguments
refscale: Add local_irq_disable() and local_irq_save() readers
refscale: Add local_bh_disable() readers
refscale: Add preempt_disable() readers
refscale: Add this_cpu_inc() readers
refscale: Add non-atomic per-CPU increment readers
refscale: Do not disable interrupts for tests involving local_bh_enable()
srcu: Create an SRCU-fast-updown API
rcutorture: Make srcu{,d}_torture_init() announce the SRCU type
refscale: Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast()
refscale: Add SRCU-fast-updown readers
Valentin Schneider (2):
rcu: Add a small-width RCU watching counter debug option
rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE
Wang Liang (1):
locktorture: Fix memory leak in param_set_cpumask()
Xuanqiang Luo (1):
rcu: use WRITE_ONCE() for ->next and ->pprev of hlist_nulls
.../RCU/Design/Requirements/Requirements.rst | 33 +-
Documentation/RCU/checklist.rst | 12 +-
Documentation/RCU/whatisRCU.rst | 3 +
include/linux/context_tracking_state.h | 44 ++-
include/linux/notifier.h | 2 +-
include/linux/rculist_nulls.h | 6 +-
include/linux/srcu.h | 147 ++++++--
include/linux/srcutiny.h | 31 +-
include/linux/srcutree.h | 99 ++++--
kernel/locking/locktorture.c | 8 +-
kernel/rcu/Kconfig.debug | 15 +
kernel/rcu/rcutorture.c | 76 ++++-
kernel/rcu/refscale.c | 379 ++++++++++++++++++++-
kernel/rcu/srcutiny.c | 13 +-
kernel/rcu/srcutree.c | 130 ++++++-
kernel/rcu/tree.c | 2 +-
kernel/rcu/update.c | 8 +-
.../testing/selftests/rcutorture/bin/kvm-again.sh | 56 ++-
.../testing/selftests/rcutorture/bin/kvm-series.sh | 116 +++++++
tools/testing/selftests/rcutorture/bin/kvm.sh | 2 +-
.../selftests/rcutorture/configs/rcu/TREE04 | 1 +
21 files changed, 1041 insertions(+), 142 deletions(-)
create mode 100755 tools/testing/selftests/rcutorture/bin/kvm-series.sh
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