From: Valentin Schneider <vschn...@redhat.com> The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, the dynticks prefix can go.
While at it, this helper is only meant to be called after failing an earlier call to rcu_watching_snap_in_eqs(), document this in the comments and add a WARN_ON_ONCE() for good measure. Signed-off-by: Valentin Schneider <vschn...@redhat.com> Reviewed-by: Frederic Weisbecker <frede...@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadh...@kernel.org> --- .../Tree-RCU-Memory-Ordering.rst | 2 +- kernel/rcu/tree.c | 23 ++++++++++++++----- kernel/rcu/tree_exp.h | 2 +- 3 files changed, 19 insertions(+), 8 deletions(-) diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst index 2d7036ad7476..7163d0def34e 100644 --- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst +++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst @@ -150,7 +150,7 @@ This case is handled by calls to the strongly ordered is invoked within ``rcu_dynticks_eqs_enter()`` at idle-entry time and within ``rcu_dynticks_eqs_exit()`` at idle-exit time. The grace-period kthread invokes first ``ct_rcu_watching_cpu_acquire()`` -(preceded by a full memory barrier) and ``rcu_dynticks_in_eqs_since()`` +(preceded by a full memory barrier) and ``rcu_watching_snap_stopped_since()`` (both of which rely on acquire semantics) to detect idle CPUs. +-----------------------------------------------------------------------+ diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 73516d76b70a..93570cb5e99e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -308,12 +308,20 @@ static bool rcu_watching_snap_in_eqs(int snap) return !(snap & CT_RCU_WATCHING); } -/* - * Return true if the CPU corresponding to the specified rcu_data - * structure has spent some time in an extended quiescent state since - * rcu_dynticks_snap() returned the specified snapshot. +/** + * rcu_watching_snap_stopped_since() - Has RCU stopped watching a given CPU + * since the specified @snap? + * + * @rdp: The rcu_data corresponding to the CPU for which to check EQS. + * @snap: rcu_watching snapshot taken when the CPU wasn't in an EQS. + * + * Returns true if the CPU corresponding to @rdp has spent some time in an + * extended quiescent state since @snap. Note that this doesn't check if it + * /still/ is in an EQS, just that it went through one since @snap. + * + * This is meant to be used in a loop waiting for a CPU to go through an EQS. */ -static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) +static bool rcu_watching_snap_stopped_since(struct rcu_data *rdp, int snap) { /* * The first failing snapshot is already ordered against the accesses @@ -323,6 +331,9 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) * performed by the remote CPU prior to entering idle and therefore can * rely solely on acquire semantics. */ + if (WARN_ON_ONCE(rcu_watching_snap_in_eqs(snap))) + return true; + return snap != ct_rcu_watching_cpu_acquire(rdp->cpu); } @@ -815,7 +826,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) * read-side critical section that started before the beginning * of the current RCU grace period. */ - if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) { + if (rcu_watching_snap_stopped_since(rdp, rdp->dynticks_snap)) { trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); rcu_gpnum_ovf(rnp, rdp); return 1; diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 137559c84309..48ad8b868d83 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -400,7 +400,7 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp) unsigned long mask = rdp->grpmask; retry_ipi: - if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) { + if (rcu_watching_snap_stopped_since(rdp, rdp->exp_dynticks_snap)) { mask_ofl_test |= mask; continue; } -- 2.40.1