[PATCH v1 05/11] rcu: Add RCU_GET_STATE_NOT_TRACKED for subsystems without expedited GPs
From: Puranjay Mohan <puranjay@kernel.org>
Date: 2026-06-24 13:24:37
Also in:
lkml, rcu
Subsystem:
read-copy update (rcu), the rest · Maintainers:
"Paul E. McKenney", Frederic Weisbecker, Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng, Uladzislau Rezki, Linus Torvalds
SRCU and Tasks RCU do not track expedited grace periods. When their callback state is checked via poll_state_synchronize_rcu_full(), the uninitialized or zeroed exp field could cause false-positive completion detection. This commit adds an RCU_GET_STATE_NOT_TRACKED sentinel value (0x2) that these subsystems can place into exp to indicate that expedited GP tracking is not applicable. The expedited sequence check in poll_state_synchronize_rcu_full() is guarded to skip entries marked with this sentinel. This is needed to allow rcu_segcblist_advance() and rcu_accelerate_cbs() to work with both normal and expedited grace periods via get_state_synchronize_rcu_full() and poll_state_synchronize_rcu_full(). Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Puranjay Mohan <puranjay@kernel.org> --- kernel/rcu/rcu.h | 13 +++++++++++-- kernel/rcu/tree.c | 3 ++- 2 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 14faa11ef23cd..39a9f6fa9a7b2 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h@@ -46,16 +46,25 @@ * the number of pending readers that will use * this inactive index is bounded). * - * RCU polled GP special control value: + * RCU polled GP special control values: * * RCU_GET_STATE_COMPLETED : State value indicating an already-completed * polled GP has completed. This value covers * both the state and the counter of the * grace-period sequence number. + * + * RCU_GET_STATE_NOT_TRACKED : State value indicating that a GP component + * is not tracked by this subsystem and should + * not be checked. Used by SRCU and RCU Tasks + * which do not track expedited GPs, to prevent + * false-positive completion when their + * gp_seq entries are checked via + * poll_state_synchronize_rcu_full(). */ -/* Low-order bit definition for polled grace-period APIs. */ +/* Low-order bit definitions for polled grace-period APIs. */ #define RCU_GET_STATE_COMPLETED 0x1 +#define RCU_GET_STATE_NOT_TRACKED 0x2 /* A complete grace period count */ #define RCU_SEQ_GP (RCU_SEQ_STATE_MASK + 1)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1d65505460bc7..095a023b19f1f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c@@ -3635,7 +3635,8 @@ bool poll_state_synchronize_rcu_full(struct rcu_gp_seq *gsp) if (gsp->norm == RCU_GET_STATE_COMPLETED || rcu_seq_done_exact(&rnp->gp_seq, gsp->norm) || gsp->exp == RCU_GET_STATE_COMPLETED || - rcu_seq_done_exact(&rcu_state.expedited_sequence, gsp->exp)) { + (gsp->exp != RCU_GET_STATE_NOT_TRACKED && + rcu_seq_done_exact(&rcu_state.expedited_sequence, gsp->exp))) { smp_mb(); /* Ensure GP ends before subsequent accesses. */ return true; }
--
2.53.0-Meta