iommu/iova: avoid softlockup in fq_flush_timeout

hulk inclusion
category: bugfix
bugzilla: 30859
CVE: NA

---------------------------

There is softlockup under fio pressure test with smmu enabled:
watchdog: BUG: soft lockup - CPU#81 stuck for 22s!  [swapper/81:0]
...
Call trace:
 fq_flush_timeout+0xc0/0x110
 call_timer_fn+0x34/0x178
 expire_timers+0xec/0x158
 run_timer_softirq+0xc0/0x1f8
 __do_softirq+0x120/0x324
 irq_exit+0x11c/0x140
 __handle_domain_irq+0x6c/0xc0
 gic_handle_irq+0x6c/0x170
 el1_irq+0xb8/0x140
 arch_cpu_idle+0x38/0x1c0
 default_idle_call+0x24/0x44
 do_idle+0x1f4/0x2d8
 cpu_startup_entry+0x2c/0x30
 secondary_start_kernel+0x17c/0x1c8

This is because the timer callback fq_flush_timeout may run more than
10ms, and timer may be processed continuously in the softirq so trigger
softlockup. We can use work to deal with fq_ring_free for each cpu which
may take long time, that to avoid triggering softlockup.
Signed-off-by: NLi Bin <huawei.libin@huawei.com>
Reviewed-By: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/iommu/iova.c

@@ -78,6 +78,7 @@ static void free_iova_flush_queue(struct iova_domain *iovad)
 
 	del_timer_sync(&iovad->fq_timer);
 
+	flush_work(&iovad->free_iova_work);
 	fq_destroy_all_entries(iovad);
 
 	free_percpu(iovad->fq);
@@ -87,6 +88,24 @@ static void free_iova_flush_queue(struct iova_domain *iovad)
 	iovad->entry_dtor = NULL;
 }
 
+static void fq_ring_free(struct iova_domain *iovad, struct iova_fq *fq);
+static void free_iova_work_func(struct work_struct *work)
+{
+	struct iova_domain *iovad;
+	int cpu;
+
+	iovad = container_of(work, struct iova_domain, free_iova_work);
+	for_each_possible_cpu(cpu) {
+		unsigned long flags;
+		struct iova_fq *fq;
+
+		fq = per_cpu_ptr(iovad->fq, cpu);
+		spin_lock_irqsave(&fq->lock, flags);
+		fq_ring_free(iovad, fq);
+		spin_unlock_irqrestore(&fq->lock, flags);
+	}
+}
+
 int init_iova_flush_queue(struct iova_domain *iovad,
 			  iova_flush_cb flush_cb, iova_entry_dtor entry_dtor)
 {
@@ -117,6 +136,7 @@ int init_iova_flush_queue(struct iova_domain *iovad,
 
 	iovad->fq = queue;
 
+	INIT_WORK(&iovad->free_iova_work, free_iova_work_func);
 	timer_setup(&iovad->fq_timer, fq_flush_timeout, 0);
 	atomic_set(&iovad->fq_timer_on, 0);
 
@@ -541,20 +561,11 @@ static void fq_destroy_all_entries(struct iova_domain *iovad)
 static void fq_flush_timeout(struct timer_list *t)
 {
 	struct iova_domain *iovad = from_timer(iovad, t, fq_timer);
-	int cpu;
 
 	atomic_set(&iovad->fq_timer_on, 0);
 	iova_domain_flush(iovad);
 
-	for_each_possible_cpu(cpu) {
-		unsigned long flags;
-		struct iova_fq *fq;
-
-		fq = per_cpu_ptr(iovad->fq, cpu);
-		spin_lock_irqsave(&fq->lock, flags);
-		fq_ring_free(iovad, fq);
-		spin_unlock_irqrestore(&fq->lock, flags);
-	}
+	schedule_work(&iovad->free_iova_work);
 }
 
 void queue_iova(struct iova_domain *iovad,

include/linux/iova.h

@@ -97,6 +97,7 @@ struct iova_domain {
 						   flush-queues */
 	atomic_t fq_timer_on;			/* 1 when timer is active, 0
 						   when not */
+	struct work_struct free_iova_work;
 };
 
 static inline unsigned long iova_size(struct iova *iova)