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Date:   Fri, 5 Oct 2018 18:33:20 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Clark Williams <williams@redhat.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] kasan: convert kasan/quarantine_lock to raw_spinlock
Message-ID: <20181005163320.zkacovxvlih6blpp@linutronix.de>
References: <20180918152931.17322-1-williams@redhat.com>
 <20181005163018.icbknlzymwjhdehi@linutronix.de>
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On 2018-10-05 18:30:18 [+0200], To Clark Williams wrote:
> This is the minimum to get this working on RT splat free. There is one
> memory deallocation with irqs off which should work on RT in its current
> way.
> Once this and the on_each_cpu() invocation, I was wondering if…

the patch at the bottom wouldn't work just fine for everyone.
It would have the beaty of annotating the locking scope a little and
avoiding the on_each_cpu() invocation. No local_irq_save() but actually
the proper locking primitives.
I haven't fully decoded the srcu part in the code.

Wouldn't that work for you?

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/kasan/quarantine.c | 45 +++++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 19 deletions(-)

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 3a8ddf8baf7dc..8ed595960e3c1 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -39,12 +39,13 @@
  * objects inside of it.
  */
 struct qlist_head {
+	spinlock_t	lock;
 	struct qlist_node *head;
 	struct qlist_node *tail;
 	size_t bytes;
 };
 
-#define QLIST_INIT { NULL, NULL, 0 }
+#define QLIST_INIT {.head = NULL, .tail = NULL, .bytes = 0 }
 
 static bool qlist_empty(struct qlist_head *q)
 {
@@ -95,7 +96,9 @@ static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
  * The object quarantine consists of per-cpu queues and a global queue,
  * guarded by quarantine_lock.
  */
-static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
+static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine) = {
+	.lock = __SPIN_LOCK_UNLOCKED(cpu_quarantine.lock),
+};
 
 /* Round-robin FIFO array of batches. */
 static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
@@ -183,12 +186,13 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
 	 * beginning which ensures that it either sees the objects in per-cpu
 	 * lists or in the global quarantine.
 	 */
-	local_irq_save(flags);
+	q = raw_cpu_ptr(&cpu_quarantine);
+	spin_lock_irqsave(&q->lock, flags);
 
-	q = this_cpu_ptr(&cpu_quarantine);
 	qlist_put(q, &info->quarantine_link, cache->size);
 	if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
 		qlist_move_all(q, &temp);
+		spin_unlock(&q->lock);
 
 		spin_lock(&quarantine_lock);
 		WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
@@ -203,10 +207,10 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
 			if (new_tail != quarantine_head)
 				quarantine_tail = new_tail;
 		}
-		spin_unlock(&quarantine_lock);
+		spin_unlock_irqrestore(&quarantine_lock, flags);
+	} else {
+		spin_unlock_irqrestore(&q->lock, flags);
 	}
-
-	local_irq_restore(flags);
 }
 
 void quarantine_reduce(void)
@@ -284,21 +288,11 @@ static void qlist_move_cache(struct qlist_head *from,
 	}
 }
 
-static void per_cpu_remove_cache(void *arg)
-{
-	struct kmem_cache *cache = arg;
-	struct qlist_head to_free = QLIST_INIT;
-	struct qlist_head *q;
-
-	q = this_cpu_ptr(&cpu_quarantine);
-	qlist_move_cache(q, &to_free, cache);
-	qlist_free_all(&to_free, cache);
-}
-
 /* Free all quarantined objects belonging to cache. */
 void quarantine_remove_cache(struct kmem_cache *cache)
 {
 	unsigned long flags, i;
+	unsigned int cpu;
 	struct qlist_head to_free = QLIST_INIT;
 
 	/*
@@ -308,7 +302,20 @@ void quarantine_remove_cache(struct kmem_cache *cache)
 	 * achieves the first goal, while synchronize_srcu() achieves the
 	 * second.
 	 */
-	on_each_cpu(per_cpu_remove_cache, cache, 1);
+	/* get_online_cpus() invoked by caller */
+	for_each_online_cpu(cpu) {
+		struct qlist_head *q;
+		unsigned long flags;
+		struct qlist_head to_free = QLIST_INIT;
+
+		q = per_cpu_ptr(&cpu_quarantine, cpu);
+		spin_lock_irqsave(&q->lock, flags);
+		qlist_move_cache(q, &to_free, cache);
+		spin_unlock_irqrestore(&q->lock, flags);
+
+		qlist_free_all(&to_free, cache);
+
+	}
 
 	spin_lock_irqsave(&quarantine_lock, flags);
 	for (i = 0; i < QUARANTINE_BATCHES; i++) {
-- 
2.19.0