From cde9070d9970eef1f7ec2360586c802a16230ad8 Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Fri, 10 May 2024 07:43:50 +0000
Subject: [PATCH] rtl88x2CE_WiFi_linux driver
---
kernel/kernel/locking/qspinlock.c | 130 ++++++++++++++++++++++++++++++-------------
1 files changed, 90 insertions(+), 40 deletions(-)
diff --git a/kernel/kernel/locking/qspinlock.c b/kernel/kernel/locking/qspinlock.c
index edd75e0..cbff6ba 100644
--- a/kernel/kernel/locking/qspinlock.c
+++ b/kernel/kernel/locking/qspinlock.c
@@ -1,15 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Queued spinlock
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
*
* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
* (C) Copyright 2013-2014,2018 Red Hat, Inc.
@@ -40,14 +31,15 @@
/*
* The basic principle of a queue-based spinlock can best be understood
* by studying a classic queue-based spinlock implementation called the
- * MCS lock. The paper below provides a good description for this kind
- * of lock.
+ * MCS lock. A copy of the original MCS lock paper ("Algorithms for Scalable
+ * Synchronization on Shared-Memory Multiprocessors by Mellor-Crummey and
+ * Scott") is available at
*
- * http://www.cise.ufl.edu/tr/DOC/REP-1992-71.pdf
+ * https://bugzilla.kernel.org/show_bug.cgi?id=206115
*
- * This queued spinlock implementation is based on the MCS lock, however to make
- * it fit the 4 bytes we assume spinlock_t to be, and preserve its existing
- * API, we must modify it somehow.
+ * This queued spinlock implementation is based on the MCS lock, however to
+ * make it fit the 4 bytes we assume spinlock_t to be, and preserve its
+ * existing API, we must modify it somehow.
*
* In particular; where the traditional MCS lock consists of a tail pointer
* (8 bytes) and needs the next pointer (another 8 bytes) of its own node to
@@ -74,12 +66,24 @@
*/
#include "mcs_spinlock.h"
-
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-#define MAX_NODES 8
-#else
#define MAX_NODES 4
+
+/*
+ * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in
+ * size and four of them will fit nicely in one 64-byte cacheline. For
+ * pvqspinlock, however, we need more space for extra data. To accommodate
+ * that, we insert two more long words to pad it up to 32 bytes. IOW, only
+ * two of them can fit in a cacheline in this case. That is OK as it is rare
+ * to have more than 2 levels of slowpath nesting in actual use. We don't
+ * want to penalize pvqspinlocks to optimize for a rare case in native
+ * qspinlocks.
+ */
+struct qnode {
+ struct mcs_spinlock mcs;
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+ long reserved[2];
#endif
+};
/*
* The pending bit spinning loop count.
@@ -101,7 +105,7 @@
*
* PV doubles the storage and uses the second cacheline for PV state.
*/
-static DEFINE_PER_CPU_ALIGNED(struct mcs_spinlock, mcs_nodes[MAX_NODES]);
+static DEFINE_PER_CPU_ALIGNED(struct qnode, qnodes[MAX_NODES]);
/*
* We must be able to distinguish between no-tail and the tail at 0:0,
@@ -112,9 +116,6 @@
{
u32 tail;
-#ifdef CONFIG_DEBUG_SPINLOCK
- BUG_ON(idx > 3);
-#endif
tail = (cpu + 1) << _Q_TAIL_CPU_OFFSET;
tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */
@@ -126,7 +127,13 @@
int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1;
int idx = (tail & _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET;
- return per_cpu_ptr(&mcs_nodes[idx], cpu);
+ return per_cpu_ptr(&qnodes[idx].mcs, cpu);
+}
+
+static inline __pure
+struct mcs_spinlock *grab_mcs_node(struct mcs_spinlock *base, int idx)
+{
+ return &((struct qnode *)base + idx)->mcs;
}
#define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
@@ -340,17 +347,23 @@
/*
* trylock || pending
*
- * 0,0,0 -> 0,0,1 ; trylock
- * 0,0,1 -> 0,1,1 ; pending
+ * 0,0,* -> 0,1,* -> 0,0,1 pending, trylock
*/
val = queued_fetch_set_pending_acquire(lock);
/*
- * If we observe any contention; undo and queue.
+ * If we observe contention, there is a concurrent locker.
+ *
+ * Undo and queue; our setting of PENDING might have made the
+ * n,0,0 -> 0,0,0 transition fail and it will now be waiting
+ * on @next to become !NULL.
*/
if (unlikely(val & ~_Q_LOCKED_MASK)) {
+
+ /* Undo PENDING if we set it. */
if (!(val & _Q_PENDING_MASK))
clear_pending(lock);
+
goto queue;
}
@@ -374,7 +387,7 @@
* 0,1,0 -> 0,0,1
*/
clear_pending_set_locked(lock);
- qstat_inc(qstat_lock_pending, true);
+ lockevent_inc(lock_pending);
return;
/*
@@ -382,13 +395,34 @@
* queuing.
*/
queue:
- qstat_inc(qstat_lock_slowpath, true);
+ lockevent_inc(lock_slowpath);
pv_queue:
- node = this_cpu_ptr(&mcs_nodes[0]);
+ node = this_cpu_ptr(&qnodes[0].mcs);
idx = node->count++;
tail = encode_tail(smp_processor_id(), idx);
- node += idx;
+ /*
+ * 4 nodes are allocated based on the assumption that there will
+ * not be nested NMIs taking spinlocks. That may not be true in
+ * some architectures even though the chance of needing more than
+ * 4 nodes will still be extremely unlikely. When that happens,
+ * we fall back to spinning on the lock directly without using
+ * any MCS node. This is not the most elegant solution, but is
+ * simple enough.
+ */
+ if (unlikely(idx >= MAX_NODES)) {
+ lockevent_inc(lock_no_node);
+ while (!queued_spin_trylock(lock))
+ cpu_relax();
+ goto release;
+ }
+
+ node = grab_mcs_node(node, idx);
+
+ /*
+ * Keep counts of non-zero index values:
+ */
+ lockevent_cond_inc(lock_use_node2 + idx - 1, idx);
/*
* Ensure that we increment the head node->count before initialising
@@ -489,16 +523,25 @@
*/
/*
- * In the PV case we might already have _Q_LOCKED_VAL set.
+ * In the PV case we might already have _Q_LOCKED_VAL set, because
+ * of lock stealing; therefore we must also allow:
*
- * The atomic_cond_read_acquire() call above has provided the
- * necessary acquire semantics required for locking.
+ * n,0,1 -> 0,0,1
+ *
+ * Note: at this point: (val & _Q_PENDING_MASK) == 0, because of the
+ * above wait condition, therefore any concurrent setting of
+ * PENDING will make the uncontended transition fail.
*/
- if (((val & _Q_TAIL_MASK) == tail) &&
- atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
- goto release; /* No contention */
+ if ((val & _Q_TAIL_MASK) == tail) {
+ if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
+ goto release; /* No contention */
+ }
- /* Either somebody is queued behind us or _Q_PENDING_VAL is set */
+ /*
+ * Either somebody is queued behind us or _Q_PENDING_VAL got set
+ * which will then detect the remaining tail and queue behind us
+ * ensuring we'll see a @next.
+ */
set_locked(lock);
/*
@@ -514,7 +557,7 @@
/*
* release the node
*/
- __this_cpu_dec(mcs_nodes[0].count);
+ __this_cpu_dec(qnodes[0].mcs.count);
}
EXPORT_SYMBOL(queued_spin_lock_slowpath);
@@ -538,4 +581,11 @@
#include "qspinlock_paravirt.h"
#include "qspinlock.c"
+bool nopvspin __initdata;
+static __init int parse_nopvspin(char *arg)
+{
+ nopvspin = true;
+ return 0;
+}
+early_param("nopvspin", parse_nopvspin);
#endif
--
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