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rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since()

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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 <vschneid@redhat.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
This commit is contained in:
Valentin Schneider 2024-04-16 17:21:25 +02:00 committed by Neeraj Upadhyay
parent 9629936d06
commit 3116a32eb4
3 changed files with 19 additions and 8 deletions
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2
Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
View File

@ -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.
+-----------------------------------------------------------------------+

23
kernel/rcu/tree.c
View File

@ -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;

2
kernel/rcu/tree_exp.h
View File

@ -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;
}