>
> 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:
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
>
