On Thu, Sep 10, 2026 at 8:16 PM Zqiang <[email protected]> wrote: > > > > > From: Kunwu Chan <[email protected]> > > > > This series rounds out atomic SRCU support with a reader-free fastpath, > > some atomic-context fixes, and additional test coverage. > > > > The core change is a reader-free fastpath for synchronize_srcu_atomic(). > > Atomic SRCU's read-side critical sections disable preemption, so when > > the summed lock and unlock counts match for both ranks, > > synchronize_srcu_atomic() can end the grace period immediately, without > > the index flip or the srcu_advance_state() scans. Correctness depends > > on the grace-period anchor written by srcu_gp_start() preceding the > > lock-count scan; two LKMM litmus tests (patches 1-2) verify that > > ordering. > > For synchronize_srcu_atomic(), the following items maybe also > need to be added:
Hi Zqiang Sent as: https://lore.kernel.org/rcu/[email protected]/ Did a small late_initcall that enters an atomic read-side critical section and calls synchronize_srcu_atomic(). srcu_lock_sync() catches it: WARNING: possible recursive locking detected swapper/0/1 is trying to acquire lock: (&ss) at: synchronize_srcu_atomic+0x28/0x380 but task is already holding lock: (&ss) at: srcu_lockdep_test_init+0xd0/0x170 *** DEADLOCK *** Rcutorture SRCU-N/P also pass. Thanks, Kunwu > > srcu_lock_sync(&ssp->dep_map); > > RCU_LOCKDEP_WARN(lockdep_is_held(ssp), > "Illegal synchronize_srcu() in same-type SRCU > read-side critical section"); > > if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) > return; > > Thanks > Zqiang > > > > > > > The series is: > > > > 1-2 LKMM litmus tests for the reader-free fastpath ordering. > > 3 srcutree: add the reader-free fastpath. > > 4 rcutorture: add --do-atomic-srcu to torture.sh. > > 5-7 srcutree: honor and propagate is_atomic so atomic SRCU never > > transitions to big. > > 8 srcutree: forbid srcu_expedite_current() on atomic SRCU. > > 9 rcutorture: disable srcu_expedite_current() for atomic SRCU. > > 10 srcutree: skip callback scheduling for atomic SRCU grace periods. > > 11 srcutree: drop the srcu_barrier() sleep for atomic SRCU. > > 12 srcutree: remove leftover debug pr_alert()s. > > 13 srcu: restrict the non_block annotation to task context, fixing a > > KCSAN data race. > > > > The KCSAN race in patch 13 is a data race on the interrupted task's > > ->non_block_count when a timer callback runs atomic-SRCU readers in > > inline softirq context. > > > > Tested with herd7 7.58 (litmus tests), torture.sh --do-atomic-srcu, and > > torture.sh --do-atomic-srcu --do-kcsan (KCSAN+PROVE_LOCKING). > > > > Kunwu Chan (13): > > litmus: Add SRCU fastpath anchor-before-scan test > > litmus: Add SRCU fastpath scan-before-anchor test > > srcutree: Add reader-free fastpath to synchronize_srcu_atomic() > > rcutorture: Add atomic-SRCU support to torture.sh > > srcutree: Honor is_atomic in check_init_srcu_struct() > > srcutree: Make init_srcu_struct_atomic() prevent transition to big > > srcutree: Don't transition atomic SRCU to big in srcu_gp_end() > > srcutree: Forbid srcu_expedite_current() on atomic SRCU > > rcutorture: Disable srcu_expedite_current() for atomic SRCU > > srcutree: Skip callback scheduling for atomic SRCU grace periods > > srcutree: Remove srcu_barrier() sleep for atomic SRCU > > srcutree: Remove debug pr_alert()s > > srcu: Restrict atomic-SRCU non_block annotation to task context > > > > include/linux/srcu.h | 10 +- > > kernel/rcu/rcutorture.c | 1 + > > kernel/rcu/srcutree.c | 95 ++++++++++++++----- > > tools/memory-model/litmus-tests/README | 16 ++++ > > .../SRCU-fastpath-anchor-before-scan.litmus | 56 +++++++++++ > > .../SRCU-fastpath-scan-before-anchor.litmus | 53 +++++++++++ > > .../selftests/rcutorture/bin/torture.sh | 24 +++++ > > 7 files changed, 229 insertions(+), 26 deletions(-) > > create mode 100644 > > tools/memory-model/litmus-tests/SRCU-fastpath-anchor-before-scan.litmus > > create mode 100644 > > tools/memory-model/litmus-tests/SRCU-fastpath-scan-before-anchor.litmus > > > > base-commit: ef15070f96c5f07de3a9b593c36f6e83bc9e3d58 > > -- > > 2.43.0 > >
