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Date:   Wed, 19 Jan 2022 07:07:54 +0000
From:   Zhou Guanghui <zhouguanghui1@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>
CC:     <will@...nel.org>, <joro@...tes.org>, <jean-philippe@...aro.org>,
        <xuqiang36@...wei.com>
Subject: [PATCH] iommu/arm-smmu-v3: fix event handling soft lockup

During event processing, events are read from the event queue one
by one until the queue is empty.If the master device continuously
requests address access at the same time and the SMMU generates
events, the cyclic processing of the event takes a long time and
softlockup warnings may be reported.

arm-smmu-v3 arm-smmu-v3.34.auto: event 0x0a received:
arm-smmu-v3 arm-smmu-v3.34.auto: 	0x00007f220000280a
arm-smmu-v3 arm-smmu-v3.34.auto: 	0x000010000000007e
arm-smmu-v3 arm-smmu-v3.34.auto: 	0x00000000034e8670
watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [irq/268-arm-smm:247]
Call trace:
 _dev_info+0x7c/0xa0
 arm_smmu_evtq_thread+0x1c0/0x230
 irq_thread_fn+0x30/0x80
 irq_thread+0x128/0x210
 kthread+0x134/0x138
 ret_from_fork+0x10/0x1c
Kernel panic - not syncing: softlockup: hung tasks

Fix this by calling cond_resched() after the event information is
printed.

Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 6dc6d8b6b368..f60381cdf1c4 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1558,6 +1558,7 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
 				dev_info(smmu->dev, "\t0x%016llx\n",
 					 (unsigned long long)evt[i]);
 
+			cond_resched();
 		}
 
 		/*
-- 
2.17.1

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