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Date: Fri, 18 Mar 2022 16:07:18 +0800
From: Zqiang <qiang1.zhang@...el.com>
To: paulmck@...nel.org, frederic@...nel.org
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/2] rcu: Call rcu_nocb_rdp_deoffload() directly after rcuog/op kthreads spawn failed
If the rcuog/op kthreads spawn failed, the offload rdp need to
be deoffload, otherwise because target rdp is considered offloaded
but nothing actually handles the callbacks.
Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
kernel/rcu/tree_nocb.h | 75 +++++++++++++++++++++++++++++++++---------
1 file changed, 59 insertions(+), 16 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 46694e13398a..e8265e4ec5ee 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -972,10 +972,7 @@ static int rdp_offload_toggle(struct rcu_data *rdp,
}
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
- if (wake_gp)
- wake_up_process(rdp_gp->nocb_gp_kthread);
-
- return 0;
+ return wake_gp;
}
static long rcu_nocb_rdp_deoffload(void *arg)
@@ -983,9 +980,18 @@ static long rcu_nocb_rdp_deoffload(void *arg)
struct rcu_data *rdp = arg;
struct rcu_segcblist *cblist = &rdp->cblist;
unsigned long flags;
- int ret;
+ int wake_gp;
+ struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
+ int condition;
- WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
+ /*
+ * The rcu_nocb_rdp_deoffload() will be called directly when
+ * rcuog/op spawn failed, because at this time the rdp->cpu
+ * is not online(cpu_online(rdp->cpu) return false), the deoffload
+ * operation was not performed on rdp->cpu, to avoid warnings
+ * add cpu_online(rdp->cpu) condition judgment.
+ */
+ WARN_ON_ONCE((rdp->cpu != raw_smp_processor_id()) && cpu_online(rdp->cpu));
pr_info("De-offloading %d\n", rdp->cpu);
@@ -1009,10 +1015,33 @@ static long rcu_nocb_rdp_deoffload(void *arg)
*/
rcu_segcblist_set_flags(cblist, SEGCBLIST_RCU_CORE);
invoke_rcu_core();
- ret = rdp_offload_toggle(rdp, false, flags);
- swait_event_exclusive(rdp->nocb_state_wq,
- !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
- SEGCBLIST_KTHREAD_GP));
+ wake_gp = rdp_offload_toggle(rdp, false, flags);
+
+ mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
+ if (rdp_gp->nocb_gp_kthread) {
+ if (wake_gp)
+ wake_up_process(rdp_gp->nocb_gp_kthread);
+
+ if (rdp->nocb_cb_kthread) {
+ condition = SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP;
+ } else {
+ /*
+ *If rcuop kthread spawn failed, direct remove SEGCBLIST_KTHREAD_CB
+ *just wait SEGCBLIST_KTHREAD_GP to be cleared.
+ */
+ condition = SEGCBLIST_KTHREAD_GP;
+ rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB);
+ }
+ swait_event_exclusive(rdp->nocb_state_wq,
+ !rcu_segcblist_test_flags(cblist, condition));
+ } else {
+ rcu_nocb_lock_irqsave(rdp, flags);
+ rcu_segcblist_clear_flags(&rdp->cblist,
+ SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ }
+ mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
+
/* Stop nocb_gp_wait() from iterating over this structure. */
list_del_rcu(&rdp->nocb_entry_rdp);
/*
@@ -1035,7 +1064,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
- return ret;
+ return 0;
}
int rcu_nocb_cpu_deoffload(int cpu)
@@ -1067,7 +1096,8 @@ static long rcu_nocb_rdp_offload(void *arg)
struct rcu_data *rdp = arg;
struct rcu_segcblist *cblist = &rdp->cblist;
unsigned long flags;
- int ret;
+ int wake_gp;
+ struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
/*
@@ -1077,6 +1107,9 @@ static long rcu_nocb_rdp_offload(void *arg)
if (!rdp->nocb_gp_rdp)
return -EINVAL;
+ if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread))
+ return -EINVAL;
+
pr_info("Offloading %d\n", rdp->cpu);
/*
@@ -1111,7 +1144,9 @@ static long rcu_nocb_rdp_offload(void *arg)
* WRITE flags READ callbacks
* rcu_nocb_unlock() rcu_nocb_unlock()
*/
- ret = rdp_offload_toggle(rdp, true, flags);
+ wake_gp = rdp_offload_toggle(rdp, true, flags);
+ if (wake_gp)
+ wake_up_process(rdp_gp->nocb_gp_kthread);
swait_event_exclusive(rdp->nocb_state_wq,
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));
@@ -1124,7 +1159,7 @@ static long rcu_nocb_rdp_offload(void *arg)
rcu_segcblist_clear_flags(cblist, SEGCBLIST_RCU_CORE);
rcu_nocb_unlock_irqrestore(rdp, flags);
- return ret;
+ return 0;
}
int rcu_nocb_cpu_offload(int cpu)
@@ -1246,7 +1281,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
"rcuog/%d", rdp_gp->cpu);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {
mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
- return;
+ goto end;
}
WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
if (kthread_prio)
@@ -1258,12 +1293,20 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
t = kthread_run(rcu_nocb_cb_kthread, rdp,
"rcuo%c/%d", rcu_state.abbr, cpu);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
- return;
+ goto end;
if (kthread_prio)
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
WRITE_ONCE(rdp->nocb_cb_kthread, t);
WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
+ return;
+end:
+ mutex_lock(&rcu_state.barrier_mutex);
+ if (rcu_rdp_is_offloaded(rdp)) {
+ rcu_nocb_rdp_deoffload(rdp);
+ cpumask_clear_cpu(cpu, rcu_nocb_mask);
+ }
+ mutex_unlock(&rcu_state.barrier_mutex);
}
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
--
2.25.1
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